


It's Raining Right Here

by kaliawai512



Series: It's Raining [1]
Category: Undertale (Video Game)
Genre: Angst, Badster, Body Horror, Brotherly Affection, Character Death, Child Death, Cinnamon Roll Papyrus, Cuddling & Snuggling, Dadster, Dysfunctional Family, Emotional/Psychological Abuse, Fluff, Gen, Happy Family, Manipulation, Medical Experimentation, Papyrus Needs A Hug, Physical Abuse, Run, Sans Needs A Hug, Suicidal Thoughts, Torture, can I warn about that character death again, if you came here from Butterscotch, upped the rating for violence
Language: English
Status: Completed
Published: 2017-06-11
Updated: 2018-03-14
Packaged: 2018-11-10 02:36:15
Rating: Mature
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 52
Words: 245,442
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11118105
Author URL: https://archiveofourown.org/users/kaliawai512/pseuds/kaliawai512
Summary: Gaster loves his sons. He loves Sans, his budding young scientist, energetic, dedicated, and ready to change the world. He loves Papyrus, his sensible, supportive, caring boy who still makes sure all of them eat three square meals and get enough sleep. He loves them more than anything else in the world, and all he wants is for them to have the life they always deserved.No matter what it t͚̫͔a̛̗̤͖̪͓̠̱͞ͅk̡̙̖̫̲̩͍͔̺̹̕e͓̤͘͜ş̪͍̺̗̕.





	1. -19

**Author's Note:**

> This story has so many inspirations I know I could never list them all. Zarla’s work, including [Handplates](http://zarla-s.tumblr.com/post/139516306171/okay-i-get-a-lot-of-questions-about-what-order-the), contributed significantly, as well as all the lovely fics about gentle-natured Dadster. And though I plotted most of this before reading talkingsoup’s [The Scientist](http://archiveofourown.org/works/5301182/chapters/12238256), once I read it, I realized that there were a number of similarities there as well. I also give a huge shout-out to [RandomCat1832](http://archiveofourown.org/users/Randomcat1832/pseuds/Randomcat1832), who supported me throughout the creation of this massive tale, and without whom I wouldn’t have even come up with this idea in the first place.
> 
> Trigger warnings throughout the story for occasionally course language, emotional abuse, physical abuse, semi-graphic torture, vague body horror, depression, possible suicidal thoughts, and major character death. Just to be completely clear, this chapter's content is not meant to be a comment on abortion or adoption. This is about one fictional character and his fictional situation and his fictional decisions. Got it? Good. 
> 
> Most chapters will definitely _not_ be this long. There was just … a lot to cover in this one. XD

Gaster took the first sip of his coffee as he pushed open the door to the lab, striding inside with the ease of one who had walked the same path for too many years to count. The dark liquid slid past his teeth and down his throat, and his brow furrowed before smoothing out in approval. Perfect. Thick and creamy, with a bit too much sugar, just the way he liked it.

The door shut behind him, and he lifted the mug to his mouth to take another sip.

Then his eyes fell on the mason jar sitting on his desk amid piles of papers, exactly where he had set it Friday before he left for the weekend.

The mug slid from his hand and shattered on the tile floor.

Gaster struggled not to choke on the coffee that had already made it into his mouth.

Inside the jar, filled with pale pink liquid, were two tiny skeletons, not even the size of his thumb.

He scrambled across the lab, his shoes crunching against the shattered ceramic. He stopped at the edge of his desk, wide-eyed and frozen, taking them in.

Yes, he could see them clearly now. And there was no mistaking it. No mistaking the little skulls, the impossibly-thin arms and legs. He leaned in further, not daring to touch his desk for fear of jostling them. Most of their features had yet to develop. There were only the beginnings of ribs attached to their spines, and the spots where their sockets should be were almost completely fused together.

But they were, without a doubt, skeletons.

Gaster grabbed his chair to keep himself from collapsing where he stood.

It was just an experiment. A silly, pointless experiment. It had taken him all of half an hour to set it up, just something to do to pass the time until his workday ended, his equivalent of a baking soda volcano, even if he supposed most other monsters would have considered it much more complex.

Just a bit of his own bone. Little scrapes, hardly enough to hurt, especially as he had a healing balm on hand to smooth on immediately after. He had had some nutrient fluid left over from last week’s failed experiment, and he hated to just throw it out since it had taken so much work to make. So he poured the fluid into a mason jar and stuck the two scrapes of bone in with it, just to see whether anything would happen.

He hadn’t had much of a hypothesis. Perhaps they would grow to slightly larger scrapes of bone, or remain stable rather than turning to dust in the absence of an associated soul. Or maybe they would still turn to dust. At least half of his pastime experiments turned up nothing of interest.

This, apparently, was not one of them.

He leaned forward, tilting his good eye closer to the jar to see them more clearly. He could barely make them out, given the color of the fluid, but there they were. Two tiny specs of light in their ribcages. The early stage of a soul.

He stood there for more than a minute, just staring, struggling to keep his legs from giving out under him as they trembled and twitched. Then he stumbled away from the desk and rummaged through the lab, his mind racing so fast that even he didn’t know what he was looking for until he found it, covered in dust underneath a pile of old blueprints from twenty years ago.

Gaster carried the large glass tube, about three feet tall, back to his desk, then, after a moment’s thought, scurried through the building to the closest sink and washed it out as thoroughly as he could. His shaking hands almost dropped the tube three times, but he always managed to regain his hold.

It wasn’t like he could find another one if it broke.

He set the cleaned tube back on his desk, using his elbow to shove the papers aside to make room. He paused then, looking at the mason jar next to the tube, back and forth between them, again and again.

All the nutrient fluid he had left was in that mason jar.

The tube was quite a bit larger than the mason jar.

If his new hypothesis was correct—and he had every reason to believe it was—these very tiny skeletons would not be so tiny in the near future.

And they would need more fluid to grow in.

Gaster’s shoulders fell.

Well. It wasn’t like he had anything pressing to finish today. And even if he did, this was quite a bit more urgent.

He didn’t look at the clock for the rest of the day. He didn’t have _time_ to look at the clock for the rest of the day. He spent every second he had looking at the notes he had made on his first batch of nutrient fluid and measuring out the correct quantities of S.E. with the magical nutrients he had taken from various kinds of monster food, mixing them together in the largest pot he had, and warming them just enough so they would blend together.

With the size of his largest pot compared to the size of the tube, he had to make three batches, but at last, the tube on his desk was almost full, leaving a little room for air at the top so that there would be no risk of the tube bursting when they grew.

When they … grew.

He shook his head as the thoughts that had remained at bay for hours began to crawl back in.

He turned again to the jar, and the tiny skeletons still floating inside. It took him more than five minutes to bring himself to unscrew the lid, as gently as he could. Nothing happened. His fingers trembled as he lifted the jar to the top of the tube and tilted it, so slowly, his soul pounding all the while, as if the movement might kill the tiny sparks of life within them.

At last, the liquid—and the minuscule creatures—tipped out into the tube with hardly a noise. The skeletons sunk, slowly, until their nature buoyancy stopped them somewhere near the middle of the tube.

The glow in their chests had not faded, and though they were far too small for him to make out many of their features, he saw no damage.

This time, when he stumbled backwards, he missed his chair entirely and crashed down to the tile floor.

If it hurt, he didn’t notice.

All he could do was stare as everything hit him all at once, ten times harder than it had that morning.

Skeletons. There were two tiny, _living_ skeletons in the tube in front of him. Skeletons that had only been shards of bone a few days ago.

Skeletons, when it had been centuries— _millennia_ —since he had last seen one other than himself.

Gaster stayed on the floor, his legs tucked close to his body, watching the tiny beings float in the fluid as if nothing mattered in the world, while he put his head in his hands, shut his eyes, and let out a shivering breath.

What in the world was he going to _do_?

*

They grew fast. Of course, he should have expected that, given their initial growth spurt, but still, every morning, he came in and measured them to find them just a little bigger, their features a little more defined.

Every morning, they looked a little more like tiny skeletons.

Every morning, it became clearer and clearer that someday, they would no longer be tiny at all.

They weren’t going to be a few scrapes of bone he threw in nutrient fluid as a silly experiment. They were going to be skeletons. They were going to be children.

_His_ children.

The second that realization hit him, he ran out of the room, all the way to the vending machine at the end of the hall. He then proceeded to bang his skull against the clear plastic until it was clear that either the plastic was going to give, or he was.

At the moment, the plastic seemed a good deal stronger than him.

He was going to have children. And they couldn’t stay in the tube forever, he would have to take them out when they got big enough. Then they would learn to walk and talk and he would have to care for them and—

He couldn’t do this. He _couldn’t._ He was a scientist. His work was everything. He had friends—even if he didn’t speak to them very much—and he didn’t mind children, but he had never spent much time around them and he didn’t even have a partner, he had never had an interest in finding a partner, and he had _never_ considered having children of his own. And these weren’t just any children. They were _skeleton_ children. When was the last time _anyone_ had seen skeleton children?

Yet here he was.

He, W.D. Gaster, was going to be a father.

He put his hands on the front of the vending machine and pushed his head away from it. He would have to make plans. He would have to … find someone. Someone who could actually take care of them. Someone who was actually _prepared_ to take care of two children, someone who didn’t spend every weekday and often a good bit of the evenings and weekends working on intricate scientific experiments. Someone who had enough common sense not to start an experiment that would turn into two _children_ in the first place _._

Gaster took a few steps back, his arms limp at his sides. He nodded to himself.

Yes. That was the only option.

Find someone else. Someone capable. And as soon as they were grown enough to remove from the nutrient fluid, he would hand them over to a competent parent and get on with his life, just like before.

But …

… would he get to see them? Would he know them at all as they grew up? Was it selfish, to want to see how the two children who grew from his own bone turned out? To see how the only other skeletons in the entire _Underground_ turned out? Would that just make it more difficult for them? Would they wonder why he gave them up? Would it be better to just pretend that he _hadn’t_ been the one to create them? Even if he did, wouldn’t they figure out the truth once they realized that there was no one else they could have been made _from_?

He put his hands to his face and groaned, thankful that, as was so often the case, he was alone in this part of the lab.

No one knew about this yet. He had time, didn’t he? Time to look for potential parents, time to figure out whether it was worth it to stay in contact once he had given them away. Time to soak in the fact that those two tiny skeletons in the tube were _his children._

He didn’t have to make any decisions yet.

He could make those later, when he felt a little less like he was going to pass out.

Gaster turned around and started back toward the lab with long, awkward strides, holding his trembling arms close to his torso and keeping his eyes ahead.

They were growing fast, but he had a few months, at least.

Certainly, by the time they were ready to be born, he could figure out what he was going to do.

*

The next few weeks, despite being some of the most hectic of his entire life, all but flashed by.

A little voice in the back of his head reminded him of the king once telling him time flew when you were watching your children grow.

He came into the lab every day, weekends included. No one was there to ask what he was doing, and he had full clearance for the entire building. He arrived early in the mornings and stayed late in the evenings, even though there were rarely any changes. They slept—if it could be called sleeping—suspended in the fluid, motionless enough that he wouldn’t have recognized them as living beings if not for the tiny pinpricks of their souls. Even though they grew rapidly, it wasn’t near fast enough for him to watch it happen with the naked eye. So logically, there was no reason for him to spend all day watching them.

That never stopped him.

And it was probably the only reason he was sitting in front of them, taking notes, when they moved for the first time.

It was quick, so quick he almost missed it, just an involuntary twitch of the leg. He pressed his face so close to the tube he almost knocked it over, his clipboard thrown to the side and his breathing fast and shaky. Of course, it took an hour for one of them to twitch again, but when they did, he smiled so wide he swore his skull nearly split in two.

He found himself wishing he had set up a camera.

His children had just moved. They were _moving._ It was just a reflex now, but soon it would be squirming and kicking and grabbing and walking and—

Then he paused, and he finally noticed how hard his soul was pounding against his ribs, the sheer _glee_ still rushing through him.

And his smile fell.

He was ridiculous. Utterly ridiculous. He was going to give them up, wasn’t he? That was the right choice. That was the _only_ choice. He wasn’t fit to be a parent. He didn’t know anything about raising children. He barely knew anything about his own kind. Yet here he was, watching the tiniest milestone with the same eager enthusiasm with which he had watched his most intricate experiments.

If he was this attached now, when they weren’t even as big as his finger …

He forced himself away from the tube after that, going back to the experiments he had neglected since that first Monday morning. He checked for new assignments—none—looked around the lab for anything unfinished—about twenty old projects, but none worth taking up—and even considered cleaning up the clutter and the dust—he hadn’t quite reached that level of desperation.

He lasted half an hour before he was back in front of the tube, watching them with eyes just as wide as before.

After that, he didn’t try again.

He tried to come up with scientific names for them, something to use to refer to them in his growing notes on their development, at least until they could speak and be given names that corresponded with their fonts—that was what skeletons usually did, wasn’t? But every time he started a note discussing the “subjects,” the “experiments,” the “units,” it made his bones squirm.

They couldn’t speak yet. Even once they were big enough to leave the fluid, it would be a while before they had heard enough spoken language to begin speaking on their own. What had skeleton parents called their children before they knew their names? Were there pet names? Affectionate, cutesy nicknames, like he had seen some monster parents use with their infants? He couldn’t remember.

He decided, rather quickly, that no names at all was better than scientific labels.

Besides, one was noticeably bigger than the other. Maybe that would change as they grew, but for now, “larger one” and “smaller one” was the best he could do. So he filled his notes with observations about the larger one twitching their legs in what Gaster was sorely tempted to call “practice kicks,” and the smaller one grasping their tiny hands around the fluid, as if they actually had the sensory development necessary to know what it felt like.

It was unscientific, and looked a bit ridiculous, especially when it filled three pages of notes. But he wouldn’t be showing this to anyone in its raw form, and besides, last time he checked, the only other person alive who could read his font was Dr. Japer, and she didn’t come in his lab much anyway.

Maybe these two little skeletons would be able to, though. From what he could remember, most skeletons only had a bit of trouble with it, like reading something with a heavy accent, even while other monsters couldn’t catch a word—and he had never met a skeleton who couldn’t understand him when he spoke. Maybe they would have illegible fonts, too. Or maybe they would get lucky and be able to communicate with the world using their voices, rather than remaining silent on reflex after so many years of using only their hands to speak.

It wasn’t until he left late that evening that he remembered that he wouldn’t be keeping them long enough to figure out their fonts at all.

*

A month into gestation, on a Tuesday, he walked into the lab to find them cuddling.

That … was really the only word he could find for it. He supposed it was inevitable that they would eventually realize they weren’t alone in their tube, since they had started moving more consciously and their living space wasn’t all that large. He had expected some tactile exploration, to be sure. But yesterday they hadn’t been touching at all, and now, apparently, they had skipped the patting of one another’s faces and clasping hands to full-on hugging, or at least what looked like hugging for two creatures not even as big as his hand.

At first, he feared that, given their early stage of development, their bones might meld together, and he considered reaching into the fluid and separating them. But when he looked closer, he saw no signs of merging. And … they looked quite content together.

He supposed they didn’t have much else to do. It was only natural that they would form a bond with another living creature in such close proximity.

So he sat down at his desk and watched them, peering close to make out the smallest of their movements. He found himself imagining them when they were big enough for regular hugs. Would they be the type of children who always wanted to sleep side-by-side? Spend every minute together? He had heard that early bonding among multiple births usually affected their relationships for the rest of their lives. Would that be the case for these two? Originally he had thought he would separate them into two tubes once they got bigger, but perhaps he shouldn’t. After adjusting to living in such close proximity to another, solitude might shock them—even upset them. He would have to work harder to find a tube big enough to hold both of them when they were the size of full-grown infants, but …

He looked closer, taking in their tiny skulls nestled together, their hands, barely detailed enough to count as hands, resting on each other’s backs.

No. He couldn’t separate them. They were clearly attached already, and besides, once they were born, they would each be the only familiar thing that the other knew. Once he—

… once he gave them up.

He wouldn’t even get the chance to _see_ how they bonded after their birth. Not very much, at any rate. And he still hadn’t decided whether he wanted to find parents who would allow him to see the children from time to time.

He hadn’t started searching for parents at all.

He should really get on that. Or at least tell someone else. Someone who could help him figure out where to start.

But …

He still had time. He didn’t have to think about that yet. It would undoubtedly be a few more months before they were ready to leave the tube, and it wouldn’t take _that_ long to find a pair of monsters willing to adopt.

For now, he could just watch them grow. Watch them develop, so similar to the skeletons he remembered. Watch them … hug, as they still were, even an hour after he arrived.

He didn’t have to think about how soon he was going to lose them.

*

The next day, they opened their eyes.

It was slow at first, and slight, like their sockets were still fused together, or they were trying to open them in an overwhelmingly bright room. Maybe it _was_ like that, to two creatures who had never seen any light at all.

For a few days after that, he found them following the motions the other made, the tilting of heads, hands patting each other’s skulls and shoulders. It was a whole new world of exploration, even though he doubted they could see more than a few inches in front of their faces. He tried to take notes, tried to jot down each stage of improvement, but far more often he found himself staring in silent, frozen wonder as they took in the light and the colors and the strange moving shape in front of them.

On Friday evening, just before he left the lab, he paused in front of their tube, leaned his face in close, and gave a small wave.

And the bigger one, who had been facing the other, turned toward the movement.

He knew it couldn’t make out his face through the nutrient fluid and the glass, its vision likely still a blur at such a distance.

That didn’t stop his soul from clenching so hard he forgot how to breathe.

He spent another two hours sitting in front of them, gesturing with his hands and fingers and watching the bigger one—and the smaller one, soon after—follow every one.

*

Two weeks later, they were growing increasingly cramped in their small tube, and he scrambled to find something else that could hold them both until they were ready to be removed from the nutrient fluid permanently. After that, of course, he had to make more nutrient fluid, which took a full day, but left him with a good deal extra.

Not that he would be doing any more experiments with that extra. He had certainly learned his lesson there.

But even once their new home was ready, it took him several hours to decide the best way to transfer them.

Tipping the tube was more difficult when he wasn’t working with a mason jar—and when the skeletons inside were significantly larger. In the end, he filled the larger tube with nutrient fluid, then carefully propped it up against an old machine he had dragged over that would hold its weight. The smaller tube was heavy, but not so heavy that he couldn’t lift it and tip it against the larger tube.

The most difficult part, without a doubt, was watching how distressed they became from the moment he began to move them.

At first, they were simply curious, looking around and following his movements as he picked up the tube. When they left the ground, they wrapped their arms around each other, clinging tighter the higher he lifted them. Their souls were developed enough now for him to grip them with magic, and he kept a gentle hold on them, ensuring they weren’t jostled too much despite the motion of the tube.

It took him more than a minute to work up the courage to tilt them, and when he did, they gripped each other tighter still. He stopped. Their grip loosened. He gritted his teeth and tried again, and still, they flinched. Finally, after five times, he took a deep breath, steeled himself, and tipped them in, still slow, still careful, but not pausing when they squeezed each other so tight that he could barely tell where one stopped and the other began.

They slipped into the fluid and sunk down, just as they had the first time he transferred them. They stopped near the middle, just like before, still clinging to each other, their heads pressed together and their eyes shut tight. Only then did Gaster release their souls. He climbed down from the ladder he had pulled out from one of the closets and stood in front of them, watching.

Slowly, very slowly, they opened their eyes and looked around. Of course, their surroundings weren’t very different—it was the same part of the lab, and the same pale pink fluid. But the glass they had grown used to was further away now, and the top and bottom of the tube must seem impossibly far to their small eyes. But they relaxed, bit by bit, and separated from each other to explore. Gaster leaned in closer. He considered pulling out one of his notebooks to write down his observations, but that could wait. He would remember what he saw, and besides, he didn’t want to be away from them for a second.

It was strange, how quickly he had grown used to having them there. How familiar their presence had become, when having someone else in his lab normally would have bothered him. Even now that they could see him, watch him as he watched them. Even now that they truly looked like very small people.

He was fairly sure they were boys at this point. With monsters like skeletons, it was impossible to tell for sure until they were old enough to express their gender identity, but from what he remembered, most parents had a good idea just by looking at them. And looking at them now, he couldn’t think of them as anything but boys.

He still had no names for them, of course. He found himself wondering, from time to time, whether he should ask their adoptive parents not to give them names until their fonts became clear, if only to keep that one skeleton tradition alive when they would, without a doubt, be the last skeletons to receive names at all.

He really should get on finding parents for them soon.

They were both still moving around, shifting in the fluid, feeling out their new home—and their final home, most likely, before they met the world properly. They stayed within a few inches of each other, kicking their legs and waving their arms and turning their heads from side to side, taking it all in.

It didn’t take the larger one very long to notice him just outside the tube.

And less than ten seconds after that, the smaller one did as well.

They had seen him before, of course. Though he doubted their vision was perfect, their eyes had been open for a while, and they had proven they could follow simple motions without a problem. But he wasn’t moving now. And they were definitely looking right at him.

After a minute, the larger one kicked their—his—little legs to move himself forward, stopping only when his hands touched the glass. The smaller one followed and found a spot just to his right, face pressed to the inside of the tube. Gaster’s soul squeezed with each tiny movement, with every second that he realized that these were _his_ children, and they were looking _at him._

He lifted his hand, and this time, the smaller one noticed the movement first, turning toward the new, probably blurry white shape. Gaster curled his fingers, then uncurled them. They both watched now, hanging on every movement, as if they were discovering a whole new world.

And they were.

“Hello,” he murmured, waving his hand back and forth, his smile growing wider by the second. The larger one tilted his head, and the smaller one just stared. A breathy laugh slipped past Gaster's throat. “Hi.”

It had been years since he had spoken to someone else and expected that they could one day understand him, even if they understood nothing now. It had been _millennia_ since there had been someone who he could actually _talk_ to. He had forgotten what it was like. He had forgotten … everything. How much would he have to relearn?

He could think about that later.

He kept waving, and they watched him, following each of his movements with far more precision, the smaller one's sockets so large now that he could already make out the beginnings of eyelights growing within.

He considered telling his colleagues exactly why he had gotten almost no work done for more than a month, and why he suspected he would finish even less in the weeks to come. Someday—when the two of them left their tube—it would be inevitable.

For now, it could wait, just a little longer.

After all, this new home had been a shock to their system, and he would be a very poor researcher if he didn't spend some time observing their adjustment.

If it involved very little note-taking and far more whispering and waving, well, no one else would ever have to know.

*

Two months into gestation, they were almost eight inches long—give or take an inch, given that they did indeed seem to be different sizes. Their features were almost as defined as those of ordinary skeleton children, from what he could remember of them, and though they still spent most of their time asleep, they moved around more, swimming through the fluid, pressing their hands and faces to the glass, and, of course, cuddling with each other.

Their increased size meant that he could keep a closer eye on their development, without needing to bring a magnifying glass up to the tube. Each day, he measured them, taking notes on their movements, their soul activity, their physical changes.

Those notes were the only reason he noticed the problem with the smaller one’s eye.

It wasn't an obvious problem. Visually, his eyesockets were identical. But Gaster found that he only responded to movement if it was made on his left side. Gaster could wave and dance around and make as many silly faces as he wanted on his right side, and the smaller one wouldn’t react until the larger one drew his attention and made him turn his head.

The conclusion was obvious after only a few tests, but Gaster did at least twenty miniature experiments before he could bring himself to accept the truth. And even then, he spent an hour staring down at his clipboard before he could write it down.

_Smaller one is blind in right eye._

He had expected it, on some level, he supposed. He had known that the condition of his own eye was hereditary, and with only one genetic contributor, it would have been far more of a shock if neither of them had visual issues.

That hadn’t stopped him from hoping. And it didn’t stop him from putting his hand, very gently, to the glass, right over the little skeleton, as if he could reach into the tube and hold him. As if there was anything he could do at all.

Everyone might be able to see that his own right eye was different than his left, but at least he could still see with it.

The smaller one’s behavior showed no other signs of problems. He was just as strong as the larger one. He moved and explored, healthy and eager to take in the world around him. He probably didn’t even notice that half of his vision was missing. He might never know the difference.

And his world would forever be half-dark.

Gaster didn’t do anything for the rest of the day after he wrote down his conclusion. He was used to that now, spending hours just sitting there, watching them. But usually he was smiling and waving and observing their each and every movement. Now, he just sat in his chair and stared, his face blank, his soul as heavy as stone.

After ten minutes, the larger one noticed him, and the smaller one a few seconds later. They pressed themselves up against the glass, peering out at him. As if in concern.

Gaster’s chest ached.

With all his energy, he lifted one hand to rest his fingers against the glass, running one fingertip over the smaller one’s head.

“I’m sorry,” he breathed, even though it was useless, even if he knew, logically, that there was nothing he could have done about the expression of unfortunate genes, even if they had been natural children. “I’m sorry.”

He said it over and over, and of course, they never understood. But they never moved away either, never got bored with his repetitive mumbling, never turned away. They stayed there, staring at him, still and worried and confused, the smaller one’s head tilted ever so slightly closer on his left side.

Long after work hours had ended, Gaster curled up in his chair, pulled his coat over him like a blanket, and fell asleep with his hand just in front of the tube.           

*

After four months, they were more than a foot long.

He spent days taking measurements of their vitals, of their behavior, of their soul activity, just to be sure that the stress of moving out of the nutrient fluid wouldn’t harm them. It would be a shock, no matter how long he waited—and if he waited long enough, they might never develop the strength to support themselves. But he had to be sure.

He couldn’t risk them. He _wouldn’t_ risk them.

Three days later, he had checked his notes ten times, and even though there was no precedent to work off of, they had reached about the same level of development as most skeleton children at birth. Probably. He didn’t really remember what most skeleton children looked like at birth, and there weren’t exactly photographs from that far back. But it was the best he could do. Nothing would ever be guaranteed, and he couldn’t wait forever.

They were awake for a good third of the day now, and though they napped regularly, they stayed awake most of the time he was in the lab. They watched him, as much as he watched them. When he waved, they made awkward movements of their tiny hands that looked like waving back. When he spoke, the larger one moved his mouth as if to mimic him, while the smaller made faint, muffled noises, as his mouth didn’t seem capable of opening, even now that the rest of him had developed.

They were active. They were curious. And they were ready to see the rest of the world.

Gaster spent one day more preparing before he actually began the process of removing them. He had thought about draining some of the fluid so he could just reach in and grab them, but that might make it even more difficult, and besides, it wouldn’t be practical with the equipment he had on hand. There was definitely no way to reach them without submerging himself in the fluid in the process. Finally, he settled on blue magic. They had experienced it once before, and it hadn’t seemed to hurt them, and besides, he would only need to use it for a few seconds each.

When the morning finally came, before he had time to question himself yet again, Gaster climbed a ladder and peered down into the tube. The skeletons tilted their heads up to look at him, even more curious than before. Gaster watched them for a few seconds, his eyes softening in fondness, his soul twisting in anxiety of what he was about to do. Then he shifted his hand and formed a loose grip around the larger one’s soul.

He held him for a few moments before he began to lift him up. The two were holding hands, but their grip was weak, and gave in after only a second’s resistance.

The larger one whimpered, and again, Gaster froze. And for a few seconds, he couldn’t move. Before he could lose focus and drop him, he shifted his hand and lifted the skeleton out of the tube, and immediately, the larger one began to squirm and fuss, while the smaller one grasped the fluid around him, his head tilted up, reaching for his—

For his brother.

That was what they were, weren’t they?

Brothers.

Gaster tucked the larger one against his shoulder, cradling him with one arm. The skeleton squirmed more, whimpers growing to hiccupped cries, but never anything louder. Confused, distressed, but nothing more. As fast—yet as carefully—as he could, Gaster lifted out the smaller one, trying three times to get him balanced in his hand without letting go of his soul and dropping him back into the fluid.

But the smaller one clung to him as best as his undeveloped motor skills allowed, as if he knew this was what he wanted. A single moment of trust that made Gaster’s soul clench before he settled the smaller one against his chest, right next to his brother.

He almost tripped on his way back down the ladder, but kept his balance, steadying his feet once more on the ground and adjusting his arms to cradle both tiny skeletons. Then he stood there, completely still, and stared down.

They were wet. They were small and wet and squirming and both of them whimpered, but quieter now, and once they grabbed onto each other, they quieted almost completely. They moved more awkwardly now, unused to open air rather than fluid, but neither of them looked in pain, or uncomfortable. With each second, they settled closer to each other, and bit by bit, they nestled against him, perhaps drawn in by his warmth, or by the thrum of another soul nearby.

Gaster couldn’t breathe.

They were alive.

They had been alive for months, of course, but now they were _here._ Out of the nutrient fluid, out in the world. Breathing. Moving. Seeing and hearing and touching and feeling.

Both of them.

Grown from simple scrapes of bone.

_His_ bone.

His genetic material.

His … children.

He was a father.

Not a father-to-be. He was a _father._ And these two tiny skeletons, snuggled against his chest and each other, were his sons.

And suddenly the idea of hunting for suitable parents had never seemed further away.

Could he have ever done that? Given them to someone else to raise, without a second thought? Could he have given up the only two other members of his species? Could he have gone a single day without worrying over their wellbeing, without wondering if they were healthy, if they were happy, if they were safe? What kind of people they would be? Their favorite foods? Their interests? Their talents?

Could he have gone a day without wishing they knew how much he loved them?

Loved them.

That was what this was, wasn't it? This pain in his chest. He had forgotten it could hurt this much. He had forgotten how much it felt like dying, how much it felt like living more than he ever had in his life.

These tiny creatures were _his._ These tiny fingers and toes, the thin, delicate ribs, the smooth skulls, the wide, curious sockets. They were grown from _him._ He had made them. He had nurtured them. He had brought them into the world.

And he couldn't let them go.

He nestled them closer, and they gripped his shirt with their tiny hands, their heads resting on his chest as their eyesockets began to slip shut. Despite the racing of his thoughts, the clenching of his soul, the overwhelming knowledge that he still had absolutely no idea what he was going to do, Gaster smiled, wider than he ever had.

Yes. These were his sons. His newborn children, with the world laid out at their feet. New skills to learn, new things to discover, new talents to develop. Two brand new people—brand new _skeletons_ —with their whole lives ahead of them.

And W.D. Gaster wasn’t going to miss a second.


	2. Chapter 1

**Notes for the Chapter:**

> *spits out various beverages in quick sequence* _Holy crap, you guys._ I had hoped you would like it but _dang_. Wow. I really can't thank you enough. That's incredible. :)
> 
> For those of you familiar with my writing (and with some little trivia for the game), some things in this chapter and onward might seem a bit ... off. There's a reason for that, I promise. I also wanted to say, for Papyrus fans: Papyrus definitely plays a significant role in this story, but this particular story is Sans-centric. Papyrus gets his time in the spotlight in the sequel, which is far more focused on him ... but that's quite a while away. ;)
> 
> Oh, and for those who aren't familiar with my updating schedule, this story will update every Thursday and Sunday. I hope you all enjoy!

“Smile!”

Sans’s permanent grin spread so wide it almost took over his whole face, and he held the large sheet of paper right under his chin, tight enough to make the edges crinkle.

The camera flashed. Then it flashed three more times, just to make sure Gaster got the best shot possible. After all, this photo would definitely be hanging in the living room. And the kitchen. And his bedroom. And probably in his office, too. And several more in case Papyrus decided to take up scrapbooking again.

And maybe he would order a few dozen copies to give out to his co-workers as well.

At his side, Papyrus cheered and clapped, and as soon as Gaster lowered the camera, he ran forward and threw his arms around his brother in a crushing hug. Sans barely managed to hold his diploma out of the way before Papyrus lifted him into the air and spun him around.

They were both laughing, and Gaster just wished that he had a video camera as well.

“You did it, brother!” Papyrus shouted, giving Sans one more quick spin before gripping him under the arms and holding him out in front of him. “I knew you could do it, no matter how many times you thought you couldn’t, I _knew_ you could and now you _did_! ”

Sans just chuckled, his eyelights like stars, his smile just as wide as before, even if he looked a little dizzy. “Thanks, Pap.”

Papyrus beamed and plopped his brother back on the ground.

“Of course!”

Sans looked to Gaster next, and for a moment, Gaster just stared back at him, taking in every detail. The curve of his smile, the bright lights of his sockets, how much taller he looked than he ever would have measured.

Then he stepped forward and pulled Sans—his son—into his arms, loosely at first, then tighter, almost tight enough to rival Papyrus. Sans hugged him back, pressing his face against his chest. Gaster rubbed a hand over his spine. He swore there were tears trying to force their way out of his sockets, and he barely managed to hold them in as he stepped away at last.

His breath trembled, and his smile hadn’t felt so wide in years.

“I would tell you I’m proud of you, but that’s been true since the day you were born,” he said, leaning down to touch his teeth to Sans’s head—or, rather, the graduation cap that still sat there. “I know how hard you worked for this, how much you wanted it. And you’ve more than earned it.”

Sans’s face had gone vaguely blue, but his eyes gleamed. “Thanks, Dad.”

Gaster said nothing else, but gave his shoulder a firm squeeze and smiled wider.

They started off toward the exit, navigating through the massive crowds of graduates and their friends and families. Several times every minute, someone would pause to greet them—or, rather, to greet Sans, laughing and patting his arm, occasionally giving his skull a quick noogie, looking like a mass of proud older siblings with their one little brother.

“Hey, congratulations, Sans!”

“You sure showed us up, kid!”

“You’re still gonna come back and tutor the rest of us, right?”

It wasn’t a surprise. After all, no one in the Underground could remember the last time a nineteen-year-old earned his doctorate. And with perfect grades, to boot.

Each time, Sans just chuckled and waved them off, making sure to tell them all the fantastic things Papyrus had been doing lately, and how he never would have made it halfway through his bachelor’s degree if his family hadn’t been there to encourage him.

Enthusiastic and talented as he was, he had never been very good at accepting compliments.

But his eyelights still grew a bit brighter, his stance a little taller, with each kind word, and Gaster found his own eyes softening, his smile stretched all the way across his face.

Once they left the building, the voices that had drowned out their own finally began to fade into the distance, and Sans pulled off his cap and gown, tucking them into Gaster’s bag, looking far more comfortable in his simple blue polo and dress shirt. He turned to Gaster with a mischievous gleam in his sockets.

“Gotta admit, Dad, I was a little afraid you weren’t gonna make it.”

Gaster raised half his browbone, incredulous.

“Sans, this is your graduation ceremony. I wouldn’t have missed it for the world.”

“You did cut it a bit close, Dad,” Papyrus added. “The president had already started her speech when you came in.”

Sans’s smile tilted into something Gaster had long learned to recognize as concerned. “You didn’t leave in the middle of anything dangerous, did you?”

Gaster looked away.

“No, no, of course not …”

“Dad.”

Gaster cleared his throat, and even though he was sure both his sons were looking at him now, he kept his gaze to the side. “I was just doing some work on a small experiment, something I started last week to pass the time …”

“Wait, the icy bracelets?!” Sans cut in, scrambling forward to force Gaster to meet his eyes. “I thought you weren’t gonna do that one!”

“Icy bracelets?” Papyrus asked. Then his browbone rose. “You mean those big ugly things that make way too much noise when you put them on? Those are dangerous!”

Gaster sighed.

“Papyrus, they’re just a small project. Many monsters who visit Hotland aren’t able to tolerate extreme temperatures, and there have been far too many cases of burns if they bump into hot metal or even approach the lava within the Core. The …”

He trailed off, searching for a good word. Sans’s worried smile looked more like a smirk.

“Icy bracelets.”

“That’s hardly a technical name, Sans,” Gaster replied.

A bigger smirk now. “When was the last time you gave anything a technical name?”

Gaster went silent for a few seconds. Then he coughed.

“All they do is trigger a cooling response when they approach extremely high temperatures, so that whatever a monster touches that would otherwise burn them is cooled before they make contact,” he went on. “They certainly aren’t hazardous.”

Sans raised half his browbone. “They turned the stove into a block of ice.”

“And they ruined my soup,” Papyrus chimed in.

“Besides, you thought of it on a Friday afternoon,” Sans finished. “You think of _all_ your crazy ideas on Friday afternoons. Or after midnight. ”

Gaster flashed him a faint, amused grin.

“I thought of the experiment that led to the two of you on a Friday afternoon.”

Sans held out a hand, palm up, as if presenting evidence to a case. “You see?”

Gaster couldn’t help a small laugh from slipping past his teeth as he shook his head.

“Well, I suppose that’s a good point.” His smile widened. “You and the icy bracelets do have plenty in common, after all.”

Sans looked at Papyrus, who looked back at him, just as confused. They turned to Gaster. “Like what?”

Gaster couldn’t quite bite back his smirk.

“You’re all very _cool._ ”

A second later, both his sons groaned so loud Gaster swore it could be heard in Snowdin.

“ _Dad._ ”

“Oh my _god,_ Dad _!_ ”

Gaster just chuckled and kept his eyes ahead.

They chattered on as they walked away from New Home, back through the Core and into Hotland. The news of Sans’s graduation had spread through most of the Underground by this point, and virtually every monster they passed had a congratulations for him—and a few of the older monsters paused to pat Gaster on the shoulder, giving him soft smiles that made him duck his head and blush.

“Like father, like son,” one of them murmured, quiet enough so the boys didn’t hear.

It was probably for the best. Sans hated comments like that, and was always quick to tell them the many ways Papyrus was like Gaster, too.

When they had passed through most of Hotland, Sans finally paused, even as Papyrus continued to ramble on about—conveyor belts, apparently, and how useful they were in building puzzles. His browbone furrowed, and he turned his head from side to side, looking around.

“Hey, Dad?”

“Yes?” Gaster replied.

“Where are we going, anyway?” Sans asked, turning back to him. “This isn’t the way home.”

Gaster’s mouth twitched up at the corners, but he managed to keep himself from smiling.

“You’ll see soon.”

Papyrus, who had stopped rambling to listen, frowned.

“That’s not an answer.” Then he paused, and his whole face lit up, like it did on their birthday when presented with a pile of wrapped gifts. “Is it a surprise?”

Sans’s browbone furrowed harder. “What, he didn’t even tell you?”

He jerked his head to face Gaster again, but Gaster just looked ahead. Sans and Papyrus exchanged baffled glances, but neither one said anything else.

Less than five minutes later, a tall, white building came into view, and their destination became obvious all on its own.

“The lab?” Sans asked, his browbone raised again.

Papyrus perked up.

“Are we going to have Sans’s celebration lunch at the lab? That seems like an odd place to eat. I thought we were going to get ice cream.”

Gaster did his very best to keep his expression neutral, but he could feel that smile tugging even harder than before. “I thought we might drop by your new workplace before we went out.”

“Dad, we go to the lab all the time,” Sans replied, walking a little faster, so it was more difficult for Gaster to hide his expression. “We practically lived here when we were little.”

Gaster hummed, dismissive.

“Yes, yes, but it’s different now that you’ve graduated. Aren’t you excited about starting your new job?”

That was all it took. Sans looked away, but he couldn’t hide the way his whole face lit up. Now that he had graduated, he was officially qualified to work at the lab, not as a visitor, not as an intern, but as a full-fledged scientist. Of course, no one was surprised. He had been accepted several months ago, but due to his overflowing class schedule, he couldn’t start work until he had finished his degree.

Not that that had stopped him from getting a head start, of course.

He had spent every minute of his very limited free time since his acceptance brushing up on his knowledge in every area of science imaginable. Gaster had assured him that he would be able to work in physics, as that was his field of study, but he insisted that he wanted to be as versatile as possible, and by now, he probably knew more about technology, biology, chemistry, and the study of magic than anyone else in the department, even if he had almost no experience—not to mention his pet passion for astronomy, which had taken up almost all of his elective courses at university despite there only being one professor who knew enough to teach it.

But lack of experience wouldn’t be an issue for long. He already had at least two dozen different ideas for how he could focus his own research, and had gone on about them so much that Papyrus had threatened to ban work-talk at the dinner table to make sure Sans actually ate his food.

Sans would be fine at the lab. More than fine. He would be brilliant.

He already was.

He didn’t ask any more questions, and he didn’t stop smiling the rest of the way to the lab.

It felt almost nostalgic, walking into the building with both his sons at his sides. Even when Sans interned here, it was just the two of them, and they often arrived and left at different times of the day. But even though his boys were far taller and older than they had been the last time, Gaster couldn’t help but imagine two tiny skeletons trailing at his side every day over school break on the days he couldn’t find a babysitter, too big to sit in their carrier but still so much smaller than him. Sometimes he wondered if time went by this fast for everyone else.

He barely managed to hide his smile as they rode the elevator down to the basement floor and started through the hallway toward the lab where he worked. Sans jittered with every step, and even Papyrus seemed enraptured, commenting on everything that had changed—and the many things that hadn’t—since he had been here last. Gaster sped up a little as they neared his lab, and Sans glanced at him, browbone furrowed, the change apparently obvious.

The first syllables of a question had already begun to leave his mouth when Gaster pushed open the lab door.

“Surprise!”

Sans jumped, Papyrus stiffened, and Gaster finally allowed the smile tugging at his mouth to curl up all the way.

In front of them, the normally-cluttered lab had been cleared out, the machines and tables and equipment pushed off to the side to make room for a single table, covered in a small pile of elegantly wrapped presents and a two-tiered yellow cake, a clumsily-drawn beaker on the icing, balloons and streamers hanging from the ceiling and scattered around the floor.

With Dr. Japer, Dr. Lemming, and Dr. Frewth, all standing behind the table, beaming.

Sans stared. He just stared, for more than ten seconds, not moving, not speaking, not even breathing, so still that Gaster wondered if he had somehow been frozen in time. Then he blinked, once, twice, and took a stumbling step back, looking around at the streamers, the balloons, the presents, the cake and the guests, taking it all in as his eyelights grew wider by the second.

“Holy—” he choked out, cutting himself off before he could finish. He shook his head, then furrowed his browbone and spun around to face Gaster again. “Dad, you sneak!”

Gaster just chuckled and shrugged.

“Well, I did say it was a bit different now. I didn’t say _how_ it was different.”

Sans groaned and rolled his eyes, but his smile remained just as wide, and he couldn’t hide his sheer glee.

On Gaster’s other side, Papyrus looked around with just as much excitement at his brother.

“Wowie! Everyone’s here!” he squealed. Then he started forward, arms out, eyes wide and glistening as they locked on one particular familiar face. “Hi, Dr. Japer! It’s been forever!”

Dr. Japer laughed and stepped around the table to meet him in a tight hug. “You really should drop by the lab more, Papyrus. We could all use a little extra _you_ around here.”

Papyrus squeezed her so tight it almost looked like it hurt. “Of course! I will gladly brighten any workspace!”

Dr. Japer just laughed again.

Sans hadn’t looked away from the whole setup, going back and forth between grinning and gawking, as if he couldn’t decide. Finally, he turned to face Gaster, his smile fallen as his browbone rose almost to the top of his skull.

“… this is all for me?” he asked, his sockets still so wide it was almost laughable.

Gaster chuckled, though his eyes remained soft and fond.

“Well, it’s not every day you get your doctorate, Sans.”

Sans floundered again, shaking his head as the table full of cake and presents, surrounded by his new co-workers, drew him in.

“But this … god, it’s …”

“Come on, Sansy, this cake’s not gonna last forever!” Dr. Lemming cut him off, having approached while Gaster wasn’t looking, giving him a pat on the shoulder so hard it almost knocked him over. “Frewth here has been eying it since we took it out, so you’d better hurry!”

“Don’t forget the presents!” Dr. Japer added, apparently having finished her hug with Papyrus, now starting back to the table.

Sans just stood there, still gawking, but Gaster managed another laugh and nudged him forward, just as Dr. Lemming pulled out the knife to begin slicing the cake.

Papyrus, as expected, did much of the talking as everyone ate their slices of cake and made makeshift toasts with glasses of soda to Sans’s accomplishment. He was all too happy to say how proud he was of his brother, and what he had been doing himself, and Sans didn’t seem to have fully come out of his state of shock. Gaster was used to being silent. It seemed that the longer he spent talking out loud to his sons, without them having any trouble understanding him, the less appealing signing became. Besides, his friends understood the important things well enough without him saying a word.

By the time the cake had been devoured and they moved on to presents, Sans was a bit more alert, and his surprise began to slip away to make room for excitement. All three of Gaster’s colleagues had brought gifts, to none of his surprise. Dr. Frewth, ever the jokester, got him a shirt that read “I Majored in Physics: To Save Time, Let’s Just Assume That I’m Always Right.” Dr. Lemming was more practical and got him a nice frame for his diploma—which, of course, would be going up on the wall as soon as Gaster had time to mount it. Dr. Japer, as Gaster should have expected, ignored the theme entirely and got him a blue hoodie, clearly used but carefully patched up, the fabric thick and soft with a fuzzy inner lining.

Sans asked what he was supposed to do with a hoodie when he lived in Hotland. Dr. Japer laughed and said that if he didn’t feel temperature much anyway, it shouldn’t make any difference if he wore a parka when visiting the Core.

Then she reminded him that his only other jacket had a hole the size of his head.

Sans rolled his eyes, but when he tried it on, his smile softened, and he gave Dr. Japer a long, tight hug.

Just as Sans set the hoodie aside, Papyrus stiffened, his browbone raised in such intense distress that Gaster’s soul stuttered and squeezed.

“Wait a second,” he said, and the entire room paused, turning to face him. “I don’t have a present!”

And just like that, the tension disappeared, so quickly it was like all the Underground had let out a sigh of relief. Sans, in particular, smiled as if an overwhelming weight had been lifted off his shoulders, and held his hands up in reassurance.

“Pap, it’s fine, you didn’t know this was gonna happen, how could you—”

“This must be remedied!” Papyrus cut him off, spinning on his heels and thrusting his hand into the air. “Fear not, dear brother, I shall return with my gift!”

Sans reached out toward him, even as he ran right through the door. “Bro, wai—”

“Let him go, Sans,” Gaster said, resting a hand on his shoulder and smiling with fond amusement. “You know he won’t be happy until he’s gotten you the best gift in the Underground.”

Sans sighed, his eyes still locked on the door, swinging shut as Papyrus’s footsteps faded down the hall.

“He didn’t need to get me anything. He already made that special dinner last night … and the special breakfast this morning. And he’s already the best brother I could ever ask for.”

Gaster just chuckled again and rubbed his shoulder through his shirt.

“Well, while we’re waiting, why don’t you open your last gift?”

Sans turned to him, then to the single present remaining on the table. His exasperation and concern disappeared, replaced by a spark of amusement gleaming deep in his sockets. “From you, I assume?”

“Well, naturally,” Gaster replied.

Sans flashed him a wider grin, shaking his head, before turning and ripping into the wrapping paper with as much enthusiasm as his five-year-old self. When he reached the box inside, he paused, just for a moment, then lifted the top and peered inside.

He stopped.

His sockets grew.

His fingers tightened around the box top in his hands.

“This … Dad …”

After a moment’s pause, he set the box top aside and reached into the box itself, lifting out the contents like he was handling glass. Gaster couldn’t help but smile wider as the brand new white coat came into full view, Sans holding it up just high enough so the ends wouldn’t touch the floor. His smile wobbled, and Gaster watched the edges of his sockets shimmer before the first few tears slid down his cheekbones.

“Gaster, you made him cry!” Dr. Frewth said, with a more than obvious grin.

Faster than Gaster would have thought possible, Sans let go of the coat with one hand and wiped at his eyes, giving Dr. Frewth his best attempt at a scowl. “I’m not crying!”

“Yeah, those look like tears, hon,” Dr. Japer said. Sans tried to glare at her, but it came out far less than intimidating. She chuckled and patted his shoulder. “Don’t worry. I cried over my first lab coat, too.”

Sans furrowed his browbone and looked away, though he couldn’t hide his overwhelming smile. “Oh, shut up, Dr. Japes.”

There were still a few tears lingering at the edges of his sockets, and he stared at the coat with the sort of wondrous joy Gaster hadn’t seen on his face since his first years in college. Dr. Frewth leaned in to elbow Sans gently in the ribs.

“Well, c’mon, try it on! I wanna see what our brand new scientist looks like!”

Sans didn’t even glare at him. He just stared for a moment before slipping his arms into the sleeves, slowly, carefully—excessively, in Gaster’s opinion, considering lab coats inevitably ended up with stains and tears—before adjusting the collar and the front flaps over his shirt.

Gaster’s soul squeezed.

Sans had tried on his lab coat countless times as a child, often trailing it over the floor for hours while he “played scientist” with his makeshift chemistry set or the science projects he had learned from that book in the library. But it had always been too big, and as little as Gaster used it himself, it had never been _his._

 _This_ coat was his. Entirely his. No one had worn it before, not any monster or human. Gaster had had it made especially for him, with measurements from all his favorite clothes, and despite Sans’s height, this coat didn’t even brush the floor. It was extremely rare to have a piece of brand-new clothing around here, not just something that had been repaired or tailored, and it hadn’t been cheap, given the lack of resources. But it was worth it. It was _more_ than worth it.

Sans turned to him, sockets wide, the faintest hint of tears at the corners of his sockets. But before he could speak, Dr. Japer wagged her finger and approached.

“Uh-uh-uh, you almost forgot the most important part.”

Sans looked at her, ready to speak, but once again, she cut him off. Not with a word, not with a gesture, but simply by holding up her hands.

Her hands, and the badge that lay in her furry palms.

A brand new white name badge, lined with blue, with his name in large letters across the middle, a bit of text below it and the official Royal Science Department seal on the top right corner.

If Sans could have opened his mouth, his jaw probably would have detached.

“Is that …?”

“Well, you do work here now,” Dr. Japer said, chuckling and pinning the badge to his coat before he had time to respond, or insist on doing it himself. “And you need something to make it official. It’s just a plain old white coat without this on it.”

Sans said nothing. If the coat had rendered him speechless, this made him shut down.

Gaster couldn’t remember the last time he had to work so hard not to break down in tears.

Dr. Japer tapped the badge with her claw before stepping back and admiring him like a fine piece of artwork, while Sans just stared down at his badge and his coat, the marks of his new position, the marks of how far he had come.

Then Dr. Lemming waved to get everyone’s attention, holding up their camera with their other hand.

“Hey, everyone, get around the table, I’m gonna get a picture!”

Sans’s head snapped up, his smile partially fallen. “Wait a sec, Papyrus isn’t back yet!”

“Sweetie, I don’t think Papyrus is going to be back for at least an hour,” Dr. Japer replied, patting his shoulder again. “Besides, we’ll make sure to get another one with him in it when he gets back.”

Sans hesitated. He glanced toward the door, as if hoping Papyrus might burst in at any second, with or without a gift in hand. But of course, he didn’t, so Sans just sighed and allowed himself a small smile once again.

“Well … alright.”

Dr. Japer grinned and walked to where Dr. Lemming was setting up the camera. Sans started to follow her, but on a reflex he couldn’t name, Gaster stepped in front of him, reaching out to adjust the collar of his coat.

“Just one second, this is crooked …”

“Dad,” Sans said, his tone unmistakable even though Gaster didn’t meet his eyes.

“And what’s that smudge on your skull?” Gaster asked, swiping a finger to clean off what he recognized as bright yellow frosting. “How did you get cake all the way up there?”

“ _Dad._ ”

Gaster paused and looked at Sans. Sans stared back with an expression Gaster was sure he had seen before. It took him several seconds to recognize it as the same face Sans had worn on that first day of college seven years before, as he stood in front of his first classroom, waiting to go in, as Gaster fussed over his clothes and checked three times to make sure he had all his supplies and his cell phone was charged and he knew to call if anything went wrong.

Bit by bit, Gaster’s shoulders fell, and he let out a long, shaky breath.

“I’m sorry,” he murmured with a faint smile. He chuckled without much humor. “It’s just … oh, goodness, now I’m really going to cry …”

His breath hitched, and he wiped away the tears that had yet to fall, in a perfect mimic of the gesture his son had inherited. Sans’s irritation disappeared, and he rested his hand on Gaster’s shoulder.

“Dad …”

“Alright, you two, you can be sappy later!” came Dr. Lemming voice, snapping them both out of their reverie and calling their attention back to the impatient blue monster waving their camera high in the air. “Come on, it’s picture time!”

Gaster sighed, his cheekbones a bit warmer than before, but Sans just snickered and slipped off to where everyone else was already gathering together for the shot.

Dr. Lemming set up their camera on one of the taller tables ten or fifteen feet away, pressing a button before scurrying back to join the rest of them. Gaster nudged Sans to the center, and though Sans grumbled, he didn’t resist, and he didn’t stop smiling.

The camera flashed once as a five-second warning, and they all grinned, Sans’s the widest of all.

Gaster allowed himself one more glance down at his son. His “scientist of the Royal Science Department” son. In his own lab coat, with his own badge, ready and determined to make his own mark on the world.

The camera flashed again, and Sans had never looked happier.


	3. Chapter 2

**Notes for the Chapter:**

> Sheesh. You guys just never stop being awesome, do ya?
> 
> Just to confirm for the comments I received: yes, Sans and Papyrus are meant to be somewhat out-of-character in this. In this tale, they ... haven't been through the things that will make them the people they are in the game yet. There's a lot of stuff yet to come. ;)
> 
> Oh, and though I can't remember all the names to give individual credit to all these people, I want to say that quite a few of the theories used in writing this story are not mine: they belong to various Tumblr users who have written some truly fantastic analyses of the game.

Sans had been awake for at least half an hour before his alarm clock went off, and when it finally buzzed, his hand slammed onto it so hard he almost knocked it off the table. A second later, he had rolled out of bed and was scrambling to pull on the outfit he had picked out the night before.

Well, Papyrus had picked out the night before, after claiming that Sans’s sense of fashion was atrocious and he needed an “expert” to show him how to dress for his first day of work.

He swung on his coat after that, taking a few seconds in front of the mirror over his dresser to adjust it. He flashed a ridiculously wide smile at his reflection. Yeah, he was a nerd. A complete and total nerd. And now he was off to get _paid_ for being a complete and total nerd, and have access to resources that would make him even _more_ of a nerd, and spend all day, five days a week, with _even more total nerds._

He scrambled out of his room and flew down the stairs, pausing just long enough to grab the bag he had packed last night before he ran out the front door. Then he kept running, faster and faster, his smile so wide it hurt, his bones stinging from the exertion, but damn it, he didn’t _care._ All he wanted to do was get to the lab.

The lab where _he_ would be working. Not just for a few weeks or months. But for a very, very long time.

He ran faster still.

Sans almost slammed into the door when he arrived. He dug his key card out of his pocket, swiped it, and burst through the doors as soon as they slid open wide enough for him to fit. Seconds later, he was in the elevator, rocking back and forth on his heels as he watched the numbers go down and down, into the basement where most of the proper labs lay.

The elevator dinged, the doors open, and Sans tripped over his own feet trying to run out into the hall outside.

He ran a bit slower, doing his best not to crash into anything important on his first day and wracking his mind to remember which turns he was supposed to take, even though he had been to the exact same lab more times than he could count. But finally, the door to his dad’s lab came into view, and Sans broke into a real, last-minute sprint.

He burst through the door, head held high, hands on his hips, smile threatening to split his skull in two.

And his eyes fell on the lab about the size of the first floor of his house, overstuffed with clutter and devoid of a single person.

He stood there for a few seconds, holding his pose, until his face began to fall from “exuberant” to “lost.” He stepped inside, letting the door fall shut behind him. He looked left. He looked right. He walked in further and looked around for a single sign of life. And he got nothing.

The lab was empty.

He looked down at his watch, tapping it twice to make sure it hadn’t frozen again. 6:42. That wasn’t _that_ early, was it? Sure, he had only seen a few other people on the way to work, so most people were probably asleep. But there was so much to do, he had so many things to go over, surely there were some projects he could get started on?

He set down his bag and searched the lab for any active experiments, anything he could at least take notes on while he waited for the others to arrive. Nothing. He knew his dad did some of his more casual experiments at home—he had named one of the spare rooms his “second lab” before Sans could remember—but he didn’t have much advanced equipment there, so anything serious or long-term would need to be stored here.

But there _wasn_ _’t_ anything here. There were a bunch of machines, tons of advanced equipment, test tubes, storage closets with materials for experiments, a computer and an overstuffed file cabinet, covered in so much dust Sans didn’t dare open it. Everything that had been pushed off to the side during his graduation party returned to its usual—messy—place. But no experiments. At least, none without a thick layer of dust on top.

He checked his watch again. 6:59. Where the hell _was_ everyone?

He checked the other parts of the basement after that. He knew his way around fairly well—it wasn’t like they had changed the layout in several decades, and he had spent a good hunk of his early childhood here, as well as all of his internship. But there was no one in any of the smaller labs or offices, or the hallways, or the break room. Just him, his footsteps echoing around the halls so loudly it almost made him uncomfortable.

Finally, he returned to his own assigned lab and paced. Back and forth, from wall to wall, examining each and every object, just in case he was missing something obvious, something that needed to be done, something _he_ could do.

Nothing.

At 7:55, he heard the faint tap of footsteps down the hall, and turned his head to see the door opening again. His dad stepped in, his furrowed browbone shooting up as soon as his eyes landed on the person standing in the center of the room.

“Sans?” he asked. He walked in the rest of the way, adjusting his bag over his shoulder. “What are you doing here so early?”

Sans stared, his mind struggling to reboot.

“I’m … here for work.”

“You don’t start until 8:30,” his dad replied, sounding more confused and concerned the closer he got.

“I … I know, but … it’s Monday!” Sans floundered, his hands gesturing helplessly as if they might do more to help him talk than his actual mouth. “Aren’t you excited to get started? Where’s everyone else? We’ve got projects to start, research to do!”

Sans paused, then looked his dad over from head to toe. He wasn't even wearing his lab coat. Granted, it had been a while since Sans had seen him in the lab, but … everyone wore their lab coats to the lab, didn't they? But his dad just wore his favorite turtleneck and simple black pants, the same as he did nearly every day at home.

His dad chuckled, half amused, half worried, as he laid his bag down on his desk.

“I believe you’ll find that Mondays are when everyone is at their slowest around here,” he replied. A tiny smile curled his mouth. “No one else is even here yet. Dr. Japer usually comes in around nine, and I wouldn’t be surprised if Dr. Frewth doesn’t arrive until almost noon. Dr. Lemming comes in early almost every day, as I'm sure you know, but they’re off today. We don’t do much work with them anyway, aside from a bit of collaboration now and then. Mostly everyone just focuses on their own projects.”

Sans kept staring, as if, if he stared long enough, he might wake up from this weird dream. His dad’s smile fell, and he stepped a little closer. His browbone rose, and he let out a soft breath, followed by another chuckle, quieter than the first.

“Goodness, Sans, graduate school didn’t wear you out at all, did it?” he asked. He shook his head, slow, disbelieving, and immensely fond. “You were exactly the same on your first day of college, up before the rest of us. Remember how I had to lock all the doors to make sure you wouldn’t leave without eating breakfast?”

His tone suggested it was a joke, but when Sans didn’t reply, his dad’s browbone creased once more.

“You _did_ eat breakfast before you left today, didn’t you?”

Sans twitched and eyed a pile of dusty test tubes on a table across the room.

His dad rubbed the spot just above his nasal cavity. When his hand fell away, he was smiling, somewhere between sad and fond.

“Well, it’s a good thing Papyrus was in a culinary mood,” he said, before opening his bag and pulling out the same metal lunchbox Sans had taken to school until his final year as an undergraduate. The rocketships painted on the front still looked pristine. “He thought you might forget to pack your lunch, so he packed you enough for three people. Eat before you get started. Trust me, your mind will function much more smoothly when fed.”

Sans looked at the lunchbox, then at his dad, his smile tight, his hands held up in near-desperation, his body still buzzing with unused energy.

“But … Dad, c’mon! We don't have time to eat, we have to get to work! Don’t we have some experiments going, some … I don’t know, what are you working on?”

His dad hummed. “Oh, I run analytics on the Core fairly regularly, and I had a few observational studies going on until recently, but … not very much, at the moment.”

Sans wasn’t sure how he could gawk when his mouth didn’t even open, but he was pretty sure he was doing a damn good job of it.

“What about the icy bracelets?”

“I told you, that was a small side project I picked up in my spare time,” his dad said. He chuckled again. “Which I have quite a bit of nowadays.”

Sans closed his sockets in a hard blink, then felt his shoulders begin to slump.

“So … what do you do at work all day?”

His dad leaned back against the closest table and stared up at the ceiling in thought.

“Well, aside from Core maintenance, the King sends in assignments from time to time, but with three other team members, those get done fairly quickly. I know Dr. Frewth has been doing a lot of work on more advanced technologies we could construct with resources available Underground, and Dr. Japer is—”

“What about stuff on the barrier?” Sans cut in, unable to keep the words from bubbling out of his throat.

His dad looked at him again, browbone furrowed.

“The barrier?”

He waited a moment, as if Sans might say something else, but when he remained silent, expectant, he looked away again.

“We haven’t done any work on the barrier in … I’m not even sure how long,” he said. “We ran into a dead end before the two of you were even born.”

Sans felt cold. Cold and … empty, and more lost than he had felt since he walked into his first university class as a twelve-year-old, short and scrawny and completely out of place.

“So you haven’t tried anything?” he asked, even though he could already guess the answer.

His dad’s expression, for once, was impossible to read.

“We tried quite a bit, believe me,” he replied. “If there was any way we could get out of here without waiting for humans to fall … it would be a great deal simpler that way. But it doesn’t seem as if there are any other feasible methods.”

He paused. He took a step closer, then another, and his face shifted to sharp concern. He tilted his head.

“Sans, was that what you were expecting to do here? Work on the barrier?”

Now it was Sans’s turn to stare at the floor. He rubbed one of his arms and shrugged.

“I mean … not _all_ the time, but I had some ideas, I … I was gonna start all these new projects, and …”

He sighed and shook his head. For a few seconds, neither of them spoke, until Sans felt his dad’s hand rest on his shoulder and give it a gentle squeeze.

“Oh, Sans …” he breathed. “I had assumed you knew by now, having interned under Dr. Lemming last year.”

“Mostly I just brought them coffee and got their tools,” Sans muttered. Screw it, he would have taken being that twelve-year-old on his first day of university over this anytime. “And I was on that weird schedule with my summer classes, but ... Besides, I just thought they were working on something different. That … there was other stuff I could work on once I …”

His dad’s hand remained on his shoulder, his thumb rubbing tiny circles through his shirt before finally falling away. He let out a long breath that didn’t quite count as a sigh.

“You know, I had to fight quite a bit to get you placed in my lab,” he said, and rather than the ache Sans expected, he instead heard a gentle fondness. He looked up, and found his dad’s mouth curled into a smile. “All the other scientists wanted you to work with them. They were sure you’d have your own space soon after you started here, so they wanted you all to themselves for as long as possible. Everyone knows you’re going to do great things.”

Sans swallowed against the growing lump in his throat. He knew his dad’s eyes had looked just as soft at his graduation ceremony, yet they struck him even more now.

“You really want to do this, don’t you?” his dad asked, with only a vague touch of concern.

Sans sighed and felt his breath tremble.

“It’s what I’ve been waiting for,” he murmured. “All these years.”

His dad’s mouth pressed tight before tilting into an even wider grin.

“Well, then. Why let some old man stop you?”

Sans chuckled, a shaky, airy sound, as his mouth curved into a hesitant smile.

“You’re not just some old man,” he murmured. His eyes gleamed. “You’re _my_ old man.”

His dad bit back a laugh.

“You’re welcome to anything in this lab,” he said, motioning toward every machine, every table, every test tube, every piece of the lab Sans had admired since before he could pronounce the names. “I don't have any projects for you at the moment, so until anything comes in, do as you please. Use that incredible mind of yours, Sans. If anyone can get us out of a dead end, it’s you.”

For a second, Sans just stared, letting the words click one by one in his head. His dad looked back at him, still smiling, silent and expectant.

Then Sans burst to life, beaming as wide as he had at his graduation ceremony, and scrambled across the room, toward the first of many devices for him to explore. The first of many experiments. The first of hundreds of ideas sparking inside his skull.

Ideas he would, for the first time, be able to bring to life.

Sans pulled out the dusty, handwritten instruction manual from behind the first machine, and as he began to read, his dad just chuckled, shook his head, and slipped out into the hallway to get his morning coffee.


	4. Chapter 3

**Notes for the Chapter:**

> Holy _crap_ , well, that happened. O.O Wow, you guys are astounding. Thank you so much!! :)
> 
> The family fluff continues! ... mostly.

Ever since the boys had stopped coming to work with him, Gaster had come to appreciate family dinners. It was the one thing he stuck to, no matter how busy things got, no matter how many projects piled up. Even if he had to go back to the lab immediately after, he was always home to have dinner with his sons.

And even though he saw Sans all day now, it was no less of a relief to eat together.

It was different, being with Sans all day and _working_ with him all day. If he was spending time with Sans on one of his days off or a weekend, he would have been talking with him, making bad jokes or sharing ideas for new projects or discussing some random topic that had sparked both their interests. And he had assumed it would be the same when Sans started working in the lab.

But he spoke with Sans almost as little now as he had before. Gaster worked on projects and assignments he received—as few as they were—and Sans spent all day, from before Gaster got to the lab until the second he left, exploring the machines gathering dust by the walls, sorting through old research and testing out the mechanisms as he jotted down notes on what Gaster presumed were ideas for his own projects and experiments. They exchanged words here and there—mainly when Gaster reminded Sans to actually _take_ a lunch break—but otherwise, even though they were in the same room, they might as well have been a mile away for how much communication actually occurred.

Even when they weren’t at the lab, Sans was working, sorting through his ideas and mumbling to himself, always carrying a notepad with him in case an idea struck. He was _happy,_ without a doubt. Gaster hadn’t seen him this excited since the first day of his internship with Dr. Lemming. But he barely rested. He barely took breaks. He raced through everything at lightning speed.

And Gaster knew, from far too much personal experience, that he couldn’t keep it up forever.

It was just a matter of whether he realized that fact by getting a little too tired, or whether he kept going until he crashed.

Gaster tried not to think about it now. It was Thursday, and even though he suspected Sans would work until the very last minute on Friday and probably try to sneak a few hours in over the weekend, at least the first week was almost over. In two days, maybe Papyrus could help him convince Sans to get some rest.

Though frankly, Papyrus seemed to be keeping plenty busy himself.

Dishes clattered and clicked together in the kitchen as Papyrus bustled about, while Gaster and Sans sat at the table, having already been shooed away when they offered to help. Neither of them had spoken since they sat down, and Gaster had taken to staring at his hands, fiddling with his fingers, and trying to think up something, _anything,_ he could suggest to do this weekend that would keep Sans’s attention off of work.

“Hey Dad?”

Gaster looked up to find Sans staring at him. “Yes?”

“Have you looked at the T.F. readings lately?” Sans asked.

Gaster’s browbone furrowed, even as he bit back a sigh. So much for doing something other than work for a few minutes.

“Not in a few weeks, no,” he replied. “I check them periodically, but there’s rarely any change. Why?”

Sans picked up his fork and played with it, tilting it back and forth without even seeming aware of the movement.

“There’s something … off about them.”

Gaster paused, thinking. Then his browbone rose.

“Oh, you mean the ripples?” he asked. Sans’s head snapped back to him. Gaster chuckled. “I must say, I’m surprised you noticed them. Most of the other scientists rarely gave them a second glance.”

Sans stared as if he had just said the other scientists didn’t know that air was a compound, or that the barrier was made of magic. “They seemed pretty obvious,” he said. “I mean, they _should_ be staying within the 4.7 to 9.3 range, but they’re all over the place.”

“That’s a very specific range,” Gaster replied, with a touch of a smile on his mouth.

Sans gave him a look. “Dad, did you even _read_ my thesis?”

Gaster chuckled and raised his glass of water to take a sip.

“Of course I did. I was on your defense committee, you remember?”

“You _were_ my defense committee,” Sans said. “I still don’t think that’s fair.”

Gaster shrugged, his smile wider. “Well, you _did_ request the current authority on your specialty. Not many people are interested in advanced theoretical physics.”

“So you know what I mean,” Sans went on, unamused, and for the first time Gaster noticed how fidgety he was. He was like that during the day, of course, that was just how he acted when he had an exciting project to work on. But he usually calmed down at least a little when they got home. “Based on every theory we’ve tested, every physical law we know of, those readings should never go outside of that range. But they _do. Every day._ Is the machine broken?”

His browbone rose, his sockets wide, eager for an answer. Gaster sighed, another chuckle slipping out of his throat.

“Those were my thoughts exactly, when I first noticed them.”

Sans straightened. “So you _do_ know about them? And you know they’re off?”

“I’ve never studied the subject as intently as you have, but yes,” Gaster replied. “The machine isn’t even as old as you are, you know. It was—”

“Dr. Billington, seventeen years ago. She designed it in under a month but it took her three years to get all the parts together.”

Gaster wondered if his smile could possibly express the fondness swelling in his chest.

“I forget how thorough you are sometimes,” he murmured, as much to himself as to Sans. Sans watched him, almost scrambling for more of a response. Gaster just leaned back in his chair, tilting his head to look at the ceiling. “She was a good friend of mine, you know. We worked together often before she retired. You remind me of her. She was one of the only people I’d met who was so fascinated with theories of spacetime, and certainly the only one willing to put in the time and effort to build a machine to measure how time and space interact.”

He met Sans’s eyes.

“She noticed something was wrong as well, from the moment she started it up. She must have checked the machine and her theories a hundred times, but they always came out the same.”

“So she saw it, too,” Sans replied, more quietly now. “There's something wrong.”

Gaster let out a breath that might have counted as a sigh.

“I have no explanation for those ripples, Sans,” he said. “Neither did she. But it's been seventeen years since that machine was completed, and nothing significant has happened here. They're certainly interesting, but I never saw any purpose to researching them when even the machine's creator couldn't figure out what they meant.”

He knew that wouldn’t be enough to satisfy his son. Nothing except for solid answers had ever been enough to satisfy him. He was far too much like Gaster in his youth to accept “we’ll never know” as a final response.

He expected disappointment. He expected irritation. He expected even a little bit of anger or ranting as to how everyone else could just not look into something they didn’t have an answer to.

What he did not expect, was sadness.

Not overt sadness. Sans rarely looked obviously _sad._ He had never been quite as expressive as his brother, and while Papyrus was more prone to a quivering mouth and teary sockets when upset, Sans just looked … low.

Now, he might as well have been several more miles Underground for the expression on his face.

“You're different now,” he muttered, with more bitterness than Gaster had heard in his voice in a long time.

Gaster straightened. “What do you mean?”

“You know what I mean,” Sans bit out, and there was the frustration, though the sadness still overpowered it by far. He shook his head and sighed. “You're … you used to be so excited about everything. when me and Pap were little, you … every time we went to the lab with you, I could _see_ it, on your face, when you talked, everything you did. It _meant_ something to you. Even if you didn't know if it would have a point, even if it was just 'cause you were curious, you always _tried._ You did things just for the hell of it. For _science._ Even if they were stupid and dangerous and they seemed ridiculous to everyone else … they meant something to you.”

He met Gaster’s eyes again, his own sockets wide, but the lights in them dim. Gaster’s soul twisted. Sans’s face pinched, even as his browbone rose.

“Seeing you like that … it was what made me wanna start learning this stuff. What made me wanna work with you.”

Gaster said nothing. He wasn’t sure there was anything _to_ say.

Dishes clattered in the kitchen, filling the silence like Gaster remembered thunderstorms once had, pattering on the roof of his home on the Surface in the middle of the night.

“What happened?” Sans asked, voice barely louder than a whisper. “Have you worked on _anything_ important since you finished the Core?”

Gaster laid one hand over the other on the edge of the table.

“Sans … I know you're determined to find a way to break the barrier, to do real good for our kind, and I couldn't be more proud of you for that,” he said, and he made no attempt to hide the affection, the love that threatened to burst from his bones. Then his breath slid out in another sigh. “And if you want to keep working on that, I will always be there to support you. But … there is only so much we can do down here, with limited resources, and a problem that's stumped monsters for centuries. Sooner or later … you have to know when to quit. When to move on to something else that is actually worth your time and energy. Worth your _talent._ ”

Sans didn't say anything at first. He looked back at Gaster, smile tight, the lights in his eyes so small they almost disappeared. And Gaster's soul twisted as he watched just a little of the spark that had driven his son for years fade.

“You're a lot of things, Dad,” he murmured. “But you're not a quitter.”

Gaster was not used to being insulted, and he knew Sans would never intentionally offend him. But he couldn't have imagined any words—or any speaker—that would have stung quite this much.

He opened his mouth.

“Ugh!” Papyrus broke in, setting down his overladen tray in the center of the table and startling both Gaster and Sans out of their silence. He frowned. “You’ve only been working in that lab four days and already you’re bringing work home with you! I thought you were done with all this when you finished your degree, Sans!”

No matter how old he got, his pouting face still didn't look any different than it had when he was a toddler. Gaster chuckled, a little more relaxed than before, and when he looked at Sans, he found him wearing just a hint of a real smile.

“You know me, bro,” he said, leaning forward to pile macaroni and cheese onto his plate. “Can't leave anything unfinished.”

Gaster nodded. “Indeed. Your brother seems to enjoy working himself _down to the bone._ ”

Sans’s skull clunked as he banged it against the table, and Papyrus smacked his hand to his face, but neither of them could quite hide their grins.

Papyrus turned his head away as he took his usual seat at the table. As each second passed, his expression softened, until at last he looked back at them and huffed.

“Hmph. Fine.” He crossed his arms and glanced back and forth between Sans and Gaster. “But this is our family time, and family time isn’t work time.”

He was still frowning, but it was less irritated now, and more … something else. Sans’s smile slipped, and Gaster’s soul twisted.

“You spent far too much time working before, Sans,” Papyrus said, quietly, staring down at the table. “Didn’t you say that you were looking forward to slacking off once you got a real job?”

Sans chuckled, though there wasn’t much humor in it. “That was a joke, Pap. All the grad students said that.”

Papyrus fidgeted, his teeth pressed in a thin line.

“Still. You need to rest sometimes.” He tightened his arms against his chest and looked up again, and suddenly, Gaster wondered how long his face had looked this desperate, and if so, how he had managed to overlook something so glaringly obvious. Papyrus’s eyes settled on Sans, his head a little higher. “And if you won’t make yourself rest, then I’ll just have to do it for you.”

His frown tilted into a smile, and he sat up taller in his chair.

“So tonight, I will tuck you in bed and read you a bedtime story.”

It was probably good that Sans hadn’t actually taken a bite of his macaroni, because even without anything in his mouth, he still choked.

“Wait, what?”

“It always helped you fall asleep before,” Papyrus replied, proud, as if the idea had somehow gotten even better in the last ten seconds.

Sans floundered, struggling to get out a word, his sockets widened to take up half his face.

“Yeah, when I was, like, five!”

“Then it should help four times as much now that you’re older,” Papyrus said. Gaster bit back the laugh trying to force its way up his throat as Papyrus scooped up twice the normal serving of peas and dumped them on Sans’s plate. “Hurry up and eat now, brother, and then it’s bedtime!”

“It's not even six!”

“You’d better hurry, bedtime is seven!”

“Pap!”

Gaster put a hand to his mouth and barely managed to muffle the snickers that slipped past his teeth.

The two of them bickered for the rest of dinner, lightly shoving one another a few times, but they never stopped smiling, and by the end of the meal, the whole family was laughing loud enough for all of Hotland to hear them.

It made the remaining tension slip from Gaster’s bones, at least for a little while.

Even if Sans still stayed up until two in the morning jotting down notes.


	5. Chapter 4

**Notes for the Chapter:**

> Thanks, everyone. Really. :)
> 
> For those of you who don't follow Butterscotch and Bones (and didn't see the announcement there), I'll be taking a one-week hiatus to catch up on some real life stuff. Next chapter will be posted on Thursday, July 6th. See you guys then!

When Gaster had arrived at the lab Friday morning, Sans was already there, and aside from a brief hello and two-word sentences, they hadn’t spoken at all in the four hours since.

It had only been a week. But Gaster had hoped, faintly, that Sans would let up on himself a little. Yet he had only dived in deeper.

Sans had always been enthusiastic, eager, and if he cared about something, he put every ounce of his energy into it. When the other kids made baking soda volcanoes for the science fair, Sans built a new temperature stabilization mechanism for Gaster’s work on the Core. When he started university, he did every extra credit project his professors offered and ended up teaching the classes when they were out sick. When Papyrus mentioned off-hand how nice it would be to try skateboarding, but how he found the terrain of Hotland too rough, Sans spent two weeks designing and building a skateboard that hovered several inches above the ground and floated over rock, dirt, snow, and even lava.

He went nights without sleeping and ran around as energetic as ever. He worked on the same project for five hours straight, until Papyrus had to pick him up and carry him away from his work. Once—thankfully _only_ once—he forgot to eat for three days when he was outlining his thesis, and only gave in and took a break when one of his classmates flung him over their shoulder and dragged him home.

Gaster had never been under any illusion that Sans wouldn’t carry all that enthusiasm over to his new job.

It had only been a week. But Gaster was beginning to believe that Sans would only stop when he ran himself into the ground.

He had put away his current project—which was really more tinkering than an actual project—half an hour ago, but Sans hadn’t noticed. Gaster leaned up against the counter and watched his son work, watched him scurry from machine to machine, jotting down notes and ideas. He must have already studied all of them by now, with special attention paid to the T.F. machine and the dust-coated S.E. extractor, but he kept going back to take more notes. Gaster wasn’t sure whether to feel worried or proud, and he had never wished more fervently that his son hadn’t taken so much after him.

“Sans?” he asked at last.

Sans squinted at the tiny, outdated screen in front of him, then wrote something down.

“Mm?”

Gaster waited for him to face him, but after twenty seconds, Sans was still staring at his work.

“I’m going to get a snack from the vending machine. Would you like anything?”

“I’m good.”

Gaster’s browbone furrowed.

“You hardly had any breakfast. Did you eat lunch?” he asked. Sans didn’t say anything, but even from a distance, Gaster could see his face tense. Gaster frowned. “Sans.”

“Fine, fine,” Sans huffed, his eyes still locked on the machine. “Maybe a candy bar or something.”

Gaster hesitated. Well, he didn’t exactly have a problem with junk food, given how much of it he ate himself. But perhaps he should take Papyrus up on the offer to make Sans a proper lunch on a regular basis, since he still had time to do it.

He slipped out of the lab with one more glance toward Sans, only to find him still engrossed in his work, peering at a machine Gaster had forgotten the name of before scratching out something on his clipboard. Gaster was caught between smiling and sighing as he made his way down the hall. He passed by Dr. Frewth on the way there, and they walked together to the vending machine, chatting about their current projects—or as close to chatting as Gaster got with how little he liked to sign—and taking turns kicking the vending machine when it refused to give them what they had purchased. Dr. Frewth was a good deal stronger than his short body suggested, and after a particularly strong and frustrated kick, he and Gaster ended up with both their purchases as well as several extra candy bars.

Gaster tried to stick the candy bars back in the vending machine, murmuring about how taking them without paying would be wrong, while Dr. Frewth just laughed.

In the end, Dr. Frewth stuck an extra few gold in the vending machine and took the candy bars to give to his new intern, and Gaster scurried off with a wave, his bag of chisps and Sans’s requested candy bar clutched in his other hand.

He was less than twenty yards from his lab when he heard the crash.

Faint, muffled from behind the door, but a very clear banging of heavy machinery against the tile floor.

Gaster dropped the food and scrambled down the hall, throwing the door open so fast he almost whacked himself in the face.

With all the clutter, it took him a few seconds to find where the sound had come from, what was off, what had happened, _why couldn’t he see Sans._ Then his eyes fell on one of the older machines in the corner, misshapen, coated in dust but still identifiable among the others. The S.E. extractor. Even taller than Gaster, with at least ten different cables running out from it, none of them plugged in, not that Gaster would have remembered where they were supposed to go after so many years without touching it.

It had fallen over. Crashed into the floor, the cords splayed out like thick strands of hair over the floor.

And in the middle of the mess, lay Sans.

Tangled in the cords, perfectly still, face-down on the floor, the edge of the machine crushing into the side of his ribcage.

Gaster stumbled and tripped twice and almost rammed right into a chair, but finally he found himself on his knees at his son’s side. He worked his fingers under the machine and lifted it just enough to shove it off to the side. Then he returned to Sans, hands hovering over him, scanning him for injuries—second and third ribs fractured, nothing fully broken—for any movement at all. It took a good ten seconds before Gaster made out the slightest hint of breath slipping through Sans’s teeth, and the knot that had twisted in his chest tight enough to strangle him loosened, just a bit.

He placed his trembling hands over Sans’s torso, closed his eyes, gathered his magic, and let it flow out.

He could feel the thrum of Sans’s soul, the hum of his magic, even as Gaster’s own mixed in to encourage it to heal him. It had been months, if not years, since he had last healed anyone, since he had last had _reason_ to heal anyone, given how Papyrus tended to jump in before he got the chance. But his bones remembered, his _soul_ remembered, and in under a minute he had settled into the rhythm, shifting his hands to either side to catch areas that might have been hurt, focusing on the cracks in his ribs where the machine had almost—

Gaster gritted his teeth, pushed the thought aside, and kept working.

At last, Sans’s HP maxed out to 40, and Gaster pulled his hands back and ignored the dizziness when he straightened. Then he sat there, silent, motionless, staring down at his son’s body and watching every breath he took, every tiny shift, his eyes squeezing shut before a groan slipped past his teeth—

Gaster stiffened.

Sans blinked open tired, heavy sockets, eyes hazy for a few seconds before they rose to meet his dad’s.

He stared. Gaster stared back. They sat there for at least a minute, just looking at each other, words passing between them without a single one spoken aloud. Finally, Sans let out a slow, heavy sigh, his sockets still drooping, his head still resting on the floor—that couldn’t be comfortable, why hadn’t Gaster thought to get him a pillow?

“Hey, Dad,” Sans murmured.

Gaster’s breath came out in a shuddering sigh, the tension slipping out of his body so fast he almost collapsed.

“You … Sans, what _happened?_ ”

Sans looked away, his cheekbones blue as he stared at the floor. He managed a small shrug. Before Gaster could say anything, he pushed himself off the ground and got to his feet. Gaster gave him room, but stayed close, ready to catch him if need be. But though Sans wobbled twice, he didn’t fall, though he never met Gaster’s eyes.

“I tripped, I guess.”

Gaster hadn’t even known his sockets could get as wide as they were now.

“Sans, you could have been killed!”

Sans huffed. “I wouldn’t’ve been _killed,_ Dad, I just fell. I fall all the time.”

“No, you don’t,” Gaster said, a bit harder than he had intended. “Not anymore.”

Sans kept staring at the wall. His face softened, little by little, until at last, his eyes shut, and he let out a long, heavy sigh.

“I don’t know, I guess … it’s a new place.” He shrugged, though Gaster could tell it pained him to say it. “It’s been a while since I had to adjust to working in a new place, and there’s a lot of stuff to trip on around here. More than I got used to in Dr. Lemming’s lab. I’m fine.”

Gaster laid a hand on his shoulder and squeezed. “You’re not fine, Sans.”

“You healed me, I’m okay,” Sans repeated, his voice tight with irritation.

“And what if I hadn’t been around to heal you?” Gaster all but snapped. He let go of Sans’s shoulder before he could risk hurting him by squeezing too hard. “What would have happened then? You were unconscious, your HP was more than halfway depleted, if that machine had fallen on you any harder …”

His breath caught in his throat, and he looked down for a moment to calm himself. When he looked back up, Sans was staring at him, his sockets wide, and much of the earlier annoyance faded away. For a few seconds, both of them just looked at each other, until last, Sans let out a long breath and shook his head.

“Look, you know how it is. You remember. Back when I was little and I ran into everything ‘cause my depth perception was all screwed up?”

Gaster remembered. He hadn’t thought about it in a while, but every now and then, his mind forced the memories back, as if to remind him how scared he had been, how panicked and disorganized and confused and _lost._ How many times he had lost track of his son in the worst possible plans. How many times he had to heal Sans, patch him up, even take him to a real physician several times to be sure there was no permanent damage.

Usually it was just bumping into furniture or walls or the doorframe. Sometimes it was tripping over cords or falling down stairs. Once, when he was four, he had toddled right over the edge of an open pit, ready to tumble into the lava below before Gaster grabbed his soul and yanked him back over the edge.

He had sat there, holding both Sans and Papyrus tight against him, for more than ten minutes after that, and he kept the boys far, far away from any ledges from then on.

It took more than two years for the image to leave his nightmares.

“It’s just like that,” Sans said, snapping Gaster’s attention back to him, back to his son, his _grown_ son, who had never looked more like his toddler self than he did at that moment. “But I’m older now, I’m bigger—okay, maybe I’m not a _lot_ bigger, but a _little_ bigger. And stronger. I know my HP’s not as high as Papyrus’s, but it’s not _low_ or anything. Plenty of monsters have the same HP as me and get hurt worse than I do, and they’re fine. I’ll figure it out, I just need time to adjust to the new environment.”

Gaster opened his mouth to speak, but found his mind blank. He wanted to pull Sans into his arms and squeeze him until they both shattered, but he couldn’t bring himself to move.

He barely noticed when Sans gave him a pat on the shoulder and a soft smile before kneeling down to start shifting the cords that had tangled on the floor. Gaster knew he should be getting down there, too, helping him move the machine out of the way so that he could actually get to the cords. But he couldn’t do anything but stare as Sans cleaned up as much of the machine as he could before going back to whatever he had been working on before.

Sans was stronger now, certainly. But that didn’t mean he was invincible. His HP was average for a monster his age, maybe a little on the low side, but most monsters weren’t half-blind—or, if they were, they had other means to make sense of their environment, or they at least weren’t working in a setting that put their safety at risk. And most half-blind monsters weren’t so enthusiastic about their unsafe work that they would forget to take the precautions necessary to keep themselves out of harm’s way.

And even if he didn’t hurt himself … he was still missing out, wasn’t he?

Even if Gaster didn’t see perfectly out of his bad eye, at least he could still see _some._ Sans … he had never known what it was like to see the world through both eyes. Gaster didn’t even _know_ how he saw the world, because to Sans, what he saw—what he didn’t see—was normal. He couldn’t describe it. It was all he had ever known.

It had been years since he had really thought about it, as much as he had considered it when the boys were young. As many times as he had thought about possible solutions. As many ideas as he had written down and thrown out before they were even half-complete, because he wasn’t willing to try anything unless it had a very high chance of success, and virtually no risk to go along with it.

Sans had been so young. So small. And Gaster refused to risk him getting hurt just for the sake of his sight.

But now …

Sans was older. Sans was stronger.

And Gaster knew so much more about him than he had nineteen years ago.

He looked at him. At his son. At one of the two most precious people he knew in the world, who went about his life as if he had never noticed his bad eye, even though Gaster had found him crying at least five times as a child, wondering why he had been born unable to see what the other kids saw.

And leaving Gaster wondering why he would be presented with yet another problem he couldn’t solve.

He pressed his mouth into a thin line and turned to his desk, cluttered with papers of half-finished ideas and projects. Nothing important. Nothing meaningful. Nothing that would really help anyone, he had spent his time inventing _icy bracelets,_ for goodness’s sake.

With one more glance at Sans to ensure he was occupied, Gaster sat down and shoved all his papers off to the side, leaving only a single notepad in front of him.

Then he picked up a pen and got to work.


	6. Chapter 5

**Notes for the Chapter:**

> [LOOK AT THIS DRAWING OH MY GOD I LOVE IT](https://www.instagram.com/p/BWIhWjvAcaI/). *cough* Thank you so much, Bohemian Kitty!!! :D
> 
> Thanks for all your kind words, everyone, and I hope you enjoy the new chapter!

It had been years since two weeks had breezed by quite this fast.

Once, time had been so obviously relative that he depended on the calendar to tell him what part of the year it was. When there was a lull in work, a day dragged on even slower than it did for his young sons, and when he was in the midst of a project, drowning in ideas, sleeping just enough to get by, keeping Sans and Papyrus in their joint carrier almost constantly, just to make sure he kept track of them, he could lose a year and barely notice it.

He hadn't realized how much he missed it.

Had it felt like this before? Had it felt this … exhilarating, to have a project that _mattered,_ something he could _do,_ something with a purpose, not just something he tinkered with because he had nothing else to do? Something that could really make a difference to one of the most important people in his life?

The last time he had felt like this was with the Core, and that had been completed six years ago.

How in the world had he managed to go without this for so long?

He slept less than two-thirds of what he did normally, but he didn’t feel tired. Every morning, he could barely wait to jump out of bed and run to the lab—and he usually did, right away, even before his sons were awake. Every evening, he went home long enough to have dinner with Sans and Papyrus before returning to the blueprints in his private office or tinkering with a part he had brought home from the lab. On several occasions, Dr. Frewth and Dr. Lemming—and especially Dr. Japer—had poked their heads into the lab throughout the day, asking whether he was alright, but he just brushed them off, saying he had work to do.

It was true. After all these years, he had real, important work to hold his attention, rather than a dozen pet projects which would never turn up anything of use.

And after two weeks, every minute of that work had finally paid off.

It was hard to tell, even after centuries, when one of his projects was truly “done,” at least until he had tested it out. And he couldn’t exactly test this one on a monster without eye problems—and he wasn’t sure if there _was_ a monster with eye problems as specific as Sans’s. He would have gladly tested it on himself, if he thought he could operate the machine while it worked on him. But the process was far too delicate, and Sans would have never forgiven him if he destroyed his eyesight completely for such a risky affair.

So he checked everything. He checked every tiny piece until he was sure it was running as well as it could, staying in the lab until almost eleven that night, examining each part five times over. And even then, he waited until morning after to say anything. Dr. Japer had once suggested that he sleep on important decisions before making them, and for once since the boys were small, he took her advice.

When he arrived at the lab the next day, Sans was already there—which he should have expected, given that he came in at a halfway normal time rather than ridiculously early as he had been since this project began. Sans looked at him, lifted a hand to wave, then went back to his work. What was he working on, anyway? Gaster hadn’t asked. It had been two weeks, and he hadn’t even noticed what his son was doing.

He had forgotten what it was like, to miss things like that.

It was one aspect he wasn’t sure he liked.

At first, he thought he might wait until Sans had reached a stopping point in his project, but after an hour, it became clear that Sans wasn’t going to reach a stopping point unless Gaster made one himself. After all, he would have gladly skipped lunch and worked long past five if Gaster didn’t step in—and this time, as far as Sans knew, he didn’t even have a reason to pause in the first place. Besides, Gaster’s eyes kept drifting to the machine sitting by the wall, blending completely with all the other machines except for the lack of dust, and he was surprised Sans hadn’t asked him about it already. It was different from the others in design as well, thin and gangly with only a control panel and screen at the base with a long arm reaching overhead. It wouldn’t be long before he noticed it on his own.

So finally, Gaster cleared his throat.

“Sans?”

Sans kept staring at the papers in front of him. “Hm?”

Gaster hesitated, once again, suddenly hit by the fact that he was really doing this. It wasn’t just an idea anymore. Not just a project he threw together because he didn’t have anything else to work on. Not one of the dozens of ideas he had tossed aside when Sans was a child. He was actually doing this. He shifted his weight and cleared his throat.

“I've been working on a new project.”

Sans glanced up at him, paused, then looked back to his work. “I know.”

Gaster stared. Then he stared some more.

“I'm sorry?”

Sans turned around to face him, half his browbone raised in such incredulity that for a moment, Gaster forgot that he was the elder of the two of them.

“Dad, you went from just running readings on the Core every day to actually _working_ on something. Something you're excited about. You're about as subtle as Papyrus when you're excited. Besides, did you _really_ think I wouldn’t see that new machine sitting by the wall when I’ve studied everything else in this lab?”

Gaster glanced away and tried, in vain, to suppress the faint blush on his cheekbones. He hadn't been able to get anything past Sans when he was a toddler, and he didn't know what had possessed him to think he could get anything past him now.

When he looked back, Sans was still waiting, a gleam of excitement shining in his sockets.

“So? What’s it for?” he asked, his voice as bright as his face. Gaster let out a shaky breath. Sans’s smile slipped down, and his brow furrowed in vague concern. “It’s not just something for the icy bracelets, is it?”

Gaster bit back a sigh.

“I told you, I was close to a breakthrough on those.”

“Papyrus said they made icicles grow inside the microwave. _While it was running._ ”

“That aside,” Gaster cut him off, clearing his throat. “I've been working on a device.”

“Yeah, we’ve established that,” Sans said, with a pointed glance toward the mechanism by the wall.

“Yes,” Gaster replied. He paused, and suddenly all his courage faded, and he looked at his son, his _son,_ and realized exactly what he was suggesting. He looked away. “I think it may be able to … heal your damaged eye.”

Silence. He waited for a second, two, three, ten, thirty. At last, he turned back, and found Sans staring at him, his face unreadable, his smile blank and his sockets wide.

“Dad … we talked about this,” Sans said at last, very quietly, very slowly, as if breaking bad news to a small child. “When I was little. You said it was genetic, there was nothing we could do about it.”

“Not then.” Gaster grit his teeth, his hands twitching into loose fists. “I wouldn't have dared risk any sort of procedure when you were so small. And you're correct, hereditary conditions are far more difficult to treat ...”

He paused, letting his sockets fall shut before they opened again, settling on his son, as sure as they were ever going to be.

“But you're older now. Stronger. Your HP has fully developed, and I have a far more thorough knowledge of your physical capabilities and limits, as well as your medical history. And you're old enough to communicate your physical state, so if something goes wrong, I can stop the process before any real damage is done.”

Sans didn't say anything, and as much as he prided himself on being able to read his sons better than anyone—save, perhaps, each other—Gaster couldn't tell what he was thinking. His shoulders slumped, and he resisted the impulse to play with the hem of his sweater.

“It … it does carry some risk. That seems unavoidable. But ...” He trailed off with a small sigh. “The potential benefit is very high. If it succeeds … you should gain at least partial vision in your right eye. Possibly full vision.”

He wanted to look away, but forced himself to meet his son’s gaze and hold it. This was his idea, and no matter what Sans said, it was his job to face it.

Sans remained silent for a very long time, his face so frozen that Gaster almost worried something was wrong with him. But at last, the tight line of his shoulders fell, just a bit, and he let out a breath he seemed to have been holding the entire time.

“That's what you've been doing. That's what you've spent all this time on,” he murmured, as much to himself as to Gaster. A tiny crease formed in his browbone. “Because of that accident?”

Gaster brought his hands close to his torso and clasped them together.

“Sans … you have no idea how many times I searched for a way to heal your eye when you were young. I never wanted you to live with my disability, especially one even more severe.” He paused, staring at his son, his little Sans, his little Sans who was _so grown up_ that he could hardly believe he was the same tiny skeleton he had pulled out of that tube nineteen years ago. He sighed. “The accident was … a reminder, of what I had forgotten. You've done such a good job adjusting to your capabilities. Did even one of your professors guess that you were half-blind?”

“I had to tell one, since she kept standing on my right side,” Sans muttered. His smile tightened, his browbone furrowed as if trying to rein himself in. “"I'm used to it. I … I've never known the difference, I guess.”

He shrugged, limp and helpless. Gaster stared at him for a moment longer, then schooled his own expression into something far more assured than what he really felt.

“I won't do this unless you agree to it, Sans,” he said, his tone absolute. “It doesn't matter how much time I've spent on this. If you say no, I won't ask again. I won't pressure you to undergo a procedure that makes you uncomfortable.”

Sans still wouldn’t look at him, and as much as Gaster wanted to step forward and pull him into a hug, to just hold him and tell him they could forget about this, he held himself back. It felt like an hour later that Sans’s shoulders slumped. He closed his eyes, took a deep breath, and lifted his head to look at Gaster.

“Okay.”

Gaster stiffened. “Sans?”

“I'll do it,” Sans said, only a faint tremor in his voice. He shifted, his smile stiff but wider than before. “I mean … I never really thought about being able to … but if I'd let anyone to do it, it would be you.”

His eyes softened, his smile more affectionate than Gaster had seen since Sans first started working in the lab. After only a second, he cleared his throat and shifted again, less anxiously this time.

“You really think this could work?”

Gaster hesitated, then nodded.

“I feel … fairly certain,” he replied. His eyes drifted again to the wall, where the device still sat, fresh and new among a practically untouched laboratory. “As certain as I can feel about an untested machine.”

Sans’s gaze followed his before shifting back. He chuckled, without much humor, and shrugged.

“Well, there's a first time for everything, right?” he asked, and though Gaster heard a touch of anxiety, it was far outweighed by unshakable confidence, and closely followed by a real smile. “I trust you, Dad.”

For a moment, Gaster forgot how to breathe.

Then he squared his shoulders, pressed his mouth into a thin line, and nodded.

“So what do I do?” Sans asked, glancing toward the machine again as if trying to figure out whether he would need to hunch under the arm of it, given that there was nothing for him to sit on.

Gaster couldn’t help a small smile, despite the sudden clenching of his soul. He motioned toward one of the tables nearby, normally used for examinations—not that he had used it for anything in years. The dust on it had been almost an inch thick before he wiped it off.

“Just lay down here. I’ll set up the machine so it’s aligned properly. The … overhead arm will emit a steady stream of magic into your eyesocket which mimics ordinary healing magic, but is more concentrated. It should trigger your own magic to activate, and create a rudimentary magical connection in your right socket. We’ll see if your body accepts the change, and … work from there.”

It sounded slightly foolish, and more than a little vague, now that Gaster said it out loud, but Sans didn’t say anything. He glanced at the table, at the device, then back to Gaster, then, with only a second’s hesitant, clambered onto the table while Gaster moved toward the machine. By the time he had begun to roll it over, Sans had already laid down, and was shifting in place.

“Try a find a spot that’s comfortable,” Gaster said, pulling the machine up next to the table. “You’ll want to be as still as possible while it’s running.”

“You could just strap me in,” Sans suggested.

Gaster stiffened, and for a few seconds he could barely meet his son’s eyes.

“I’m not going to _strap_ you to a _table,_ Sans.”

Sans just shrugged, as if he had suggested painting a red dot on his forehead. “It might help.”

Gaster’s mouth pressed together so hard it almost hurt.

“Just do your best to stay still, and keep your eyes open. Your sockets are large, so it doesn’t need to be as precise as it might be for other monsters.”

Sans gave him a look, but settled down without further complaint. Gaster rolled over a second, older machine and attached several wires to different parts of his body, mostly close to his soul—basic monitoring systems to ensure that he remained stable throughout the entire procedure. He gave the display screen only a glance, to ensure that it was taking a baseline reading of Sans’s vitals, the little light on the side glowing green. Then he turned to the new device—he really needed to pick a name for it—and began aligning it to Sans’s position on the table. He felt Sans’s eyes on him the whole time, and even though his gaze was interested, curious, rather than suspicious, Gaster couldn’t help but feel something in his bones prickling.

It would be alright. He had planned for all of this. Everything was going to be fine.

Sans would be able to see. At least … at least a little bit.

After five minutes—and ten measurements to be sure—the machine was perfectly aligned, and Sans had apparently found a spot that didn’t tempt him to shift every few seconds. Everything was prepared, but Gaster found himself pausing. Thinking. Staring down at Sans, his _son,_ resting on an operating table, hooked up to a machine.

He was really doing this. The very thing he had told himself almost two decades ago simply could never be done safely, and he was doing it.

This wasn’t just some pastime experiment. This was his _child._ And he could not mess this up.

He swallowed hard and rested a hand on the machine, near the control panel.

“Are you ready?”

Sans flashed him a wide, shaky grin.

“Fire it up.”

Gaster swallowed again, looking away from Sans and back to the control panel. He checked each of the settings three times, feeling Sans’s eyes following his every movement, probably already figuring out how the machine worked. He glanced at the overhead arm, aimed straight into Sans’s right socket, then at Sans, one more time. Gaster took a deep breath and hovered his fingers over the big green button at the bottom of the panel.

Then he pressed it.

The machine hummed. Sans froze in place, even stiller than before, and stared ahead, eyes wide open.

Gaster counted down in his head, every bone so stiff it felt like he would never move again.

The tip of the arm lit up, and a thin laser shot through the empty air, right into Sans’s socket.

It was, perhaps, the most terrifying moment of Gaster’s life. He knew it would happen, he had _built_ this machine, it was doing exactly what it was meant to do, but this was still his son, resting on a table while a laser burned into his eyesocket.

He glanced at the monitor. Light still green. Still stable. Sans was tense, clearly a little uncomfortable, but that was to be expected, it would be alright, it shouldn’t be very painful, this was just as he had expected. All it would take was a few minutes, a few minutes for the magic of the laser to trigger the magic in Sans’s soul, a few minutes and his eye would be fixed, he would be able to _see,_ all of this would be worth it and he could finally experience everything Gaster had wished for him since before he was born—

_Beep._

Gaster flinched and looked down at the machine.

_Beep beep. Beep beep beep beep._

Red.

The light on the monitor was flashing red.

And suddenly the beeping was a single, high-pitched cry, the monitor screen flashing, and Gaster was moving before he had time to think.

No. No no no no _no._

He pressed the kill switch five times, even after he heard the machine begin to power down. As soon as the laser was clear, he shoved it out of the way. It crashed into the floor, the metal arm snapping off, but he didn’t care, he had to get to Sans, Sans, Sans, _Sans._

Sans wasn’t moving, his body tense, his smile tight and his sockets squeezed shut.

And Gaster barely needed to glance at his HP to see it well into single digits.

Just like he had two weeks before—only _two weeks before_ —he gathered up his magic and rested his hands on Sans’s skull, forcing the energy out into his bones. There were no visible injuries, that might not even be where the damage was, but he had to start somewhere, he had to help him, he had to fix this.

Fix this.

Fix Sans’s eye.

He had been trying to fix Sans’s eye, and now he was … he …

… because of _him_ …

Stupid. Stupid, stupid, _stupid,_ he should have _tested_ it, on himself, on _anything,_ he should have prevented this, he should have seen it coming, he had put his _son_ in danger, how could he even _think_ of trying something so new, so experimental, without even—

The magic around his hands flickered, and he forced his mind back on track, as much as he wanted to berate himself for the next few hours. He closed his eyes and let the magic flow out of him and into his son’s body, his skull, his ribcage, his soul, healing the damage as best he could.

He felt Sans’s HP begin to rise, just as he watched the tension in his body fade. A soft, relieved breath slipped past his teeth before he went limp against the table, his face relaxed in sleep.

Gaster didn’t pull his hands away for five more minutes, and when at last he stepped back, he almost fell to the floor.

Healing Sans two weeks ago had been a cakewalk compared to how drained he felt now. But Sans’s HP was almost fully restored, and Gaster would have gladly fallen unconscious if would have helped his son recover faster.

But as it was, all he could do was wait.

And, apparently, pace.

Even though his legs threatened to give out any second, Gaster couldn’t stop moving. Couldn’t stop thinking. He had done this to help his son, and he could have killed him. All because he had some silly idea for some silly experiment even though so many of his experiments failed the first time around, and when they didn’t, it was usually by accident. He should have waited longer. He usually waited for important things, to give himself time to notice mistakes, so _why hadn’t he done that for something this important._

Sans could have been hurt, far worse than he had already been. He could have … all because Gaster …

He stopped in front of the fallen machine, his hands curled into fists. He wanted to destroy it. He wanted to tear it into scrap metal and toss it in the dump, even though he knew how much of a waste it would be, when supplies were already limited. Still, he allowed himself one small kick, right near the control panel.

And winced.

The machine wasn’t even dented, and it felt like he had just cracked one of his toes.

Sans would have been laughing his head off right now.

Gaster paused, finally taking a moment to catch his breath, to stop, to _think._ Nothing he could do to this stupid machine would help now. The procedure had failed. Sans would be alright, after a few days. Gaster had been an idiot, but at least he knew how to avoid being the same type of idiot in the future. He turned back to Sans, ready to sit by his side until he finally woke up and the two of them could go home and forget this stupid mess.

Then he stopped again, his eyes on the monitoring device.

The monitoring device he had never unhooked.

He hadn’t even thought of it until now. It hadn’t been doing any damage, even if it hadn’t been helping after the initial alarm—when had that gone quiet?—so he had seen no reason to remove it while he healed Sans. It was an old machine, half-broken, it wouldn’t even do printouts or analyses, all it did was take a baseline reading of a monster’s vitals when they were first hooked up, and sound an alarm if those numbers rose or fell too far.

It was still taking readings now. Still measuring the output levels of Sans’s soul, the vital signs of his magic coursing through his bones.

Sans had never been hooked up to a machine like that before. There had never been a reason. And Gaster hadn’t been paying attention to the numbers before the procedure. Just the fact that it was functioning, that it had taken a baseline and would warn him if anything went wrong.

There was no warning signal going off now, so apparently the numbers had returned to their baseline.

Except …

… that wasn’t the baseline of a skeleton soul.

Or at least … it _shouldn’t_ be.

It had been years—more than two thousand years—since he had seen another skeleton, and they had all died long before such machines were invented. And as a scientist, he would be loathe to use only _himself_ as an example of all skeletons. But this wasn’t a slight fluctuation, the sort of differences that might be expected between individuals of the same species. Those numbers were … off. Very off.

And …

He had _seen_ numbers like those before. A long time ago, before either of the boys were born, back when the last—

He scrambled across the room, yanking open the drawer of his old file cabinet so hard it almost came loose. It had been at least five years since he had opened it, he could barely remember where anything was, the top was covered in dust and he couldn’t read the labels and he was probably tearing the papers as he rifled through them, but he didn’t care. Where was it? He had put it in here, somewhere in this cabinet, it had to be here, he was a shameless packrat, he never threw _anything_ away—

There.

The green folder, tucked away in the back, the edges bent and the writing on top so faded he couldn’t make it out.

But he didn’t need to.

His movements far more careful, he pulled the folder out and slid the drawer shut.

He carried the folder back to the table, opened it, and wiped the dust off the front page enough to read the numbers he had scratched out decades ago. His handwriting had been even worse then. Granted, he hadn’t been in the best emotional state, either. It wasn’t exactly the most pleasant series of experiments he had performed, and the king himself had come by to insist Gaster take two weeks off after all was complete. And though he had initially poured through the readings, searching for anything that could be useful, after more than a year of no results, he had filed the folder away to collect dust with the rest of his failed experiments.

Information on the behavior, biology and soul of a living human had seemed so invaluable at the time, and he had been all too disappointed to find it virtually worthless.

He peered down at the screen again, reading the numbers to himself before returning to the numbers on the first page of the file.

He checked again.

And again.

And one more time after that.

Then he just stood there, looking down at the paper as if it just come alive and bitten him.

It wasn’t a match. Not perfect, not by any means, but … it was close. The numbers measuring the activity of Sans’s soul were notably closer to the _human’s_ soul than they were to Gaster’s.

Gaster lifted his head and looked at his son, still unconscious on the table, calm and safe and healed. Breathing slowly and easily, the bones of his face smoothed out, just like he had looked nearly every day for the past nineteen years.

He had always suspected that something about his boys would be different. They were made differently, after all, and it was only natural that _some_ parts of their biology would be different from what he expected of a natural-born skeleton. It had never mattered to him. They were still his children, regardless of how they had come into the world. He had never treated them any differently, and though they knew that they had been grown in tubes—as awkward a conversation as it had been, he wasn’t going to let them find out any other way—they had never considered themselves any different from other monsters.

And as far as Gaster had known, until now, they hadn’t been.

Not in any way he would ever find out.

But now he _had_ found out. The information was right here in front of him. His son’s soul resembled a human soul, even if there were still significant differences. And if he could create a monster soul— _two_ monster souls—that were this similar to human souls, without even trying … if he actually _did_ try, if he put this knowledge to use, if he could do more research, if he could see exactly how close a monster soul could get to a human’s, if he could _replicate_ it …

Gaster clenched his teeth.

No. He had given up on this. He had given up on this _decades_ ago. He had tried, he had researched, he had looked for any possible way to make it happen, but it _couldn’t be done._ He didn’t have enough to work with, and even if he could use what he _did_ have, it wouldn’t be enough. The composition of monster and human souls was just too different.

But …

That had been before. Back when he had assumed that all monster souls were necessarily similar to one another. Back when there had never been an artificial monster grown in a unique nutrient fluid. Back when he had never _imagined_ that the essence he extracted from those human souls would actually be put to _use,_ in however accidental a way.

Nineteen years ago, when he had been far too focused on the fact that he now had two children to wonder whether the fluid they were grown in would make them truly different.

“… Dad …?”

Gaster’s head snapped up, and he jerked around to face the table. Sans tilted his head so Gaster could make out his half-lidded sockets. In a second, Gaster was at his side, checking him over, murmuring to himself, to Sans, to nobody in particular, asking him questions to make sure that his healing had worked and there was no lasting damage.

It was much, much easier to stay busy, much easier to focus on the here and now.

Much easier to think of something he knew he _had_ to do rather than the thoughts brushing the back of his mind.

He didn’t say anything about the results, and before Sans woke up fully, Gaster slipped the green file into the back of a random drawer. He could deal with that later. His son was the priority. His son had always been, and would always be, the priority.

Despite Sans’s protests, they went home as soon as he could stand, Sans leaning on Gaster as they made their way back to the house. When Sans finally asked what had happened, Gaster explained, and though a touch of disappointment flashed across Sans’s face, he shrugged it off and went back to smiling, more tiredly than usual. Papyrus made them an early, special dinner, “filled with everything you need to feel better soon, Sans, even though you won’t tell me why you’re hurt in the first place,” and they gathered on the couch to watch one of the DVDs Gaster had picked up from the garbage dump a few weeks before. They cuddled together and smiled and laughed, as if nothing had changed.

But every few minutes, Gaster’s eyes drifted to his sons, one on each side of him, and he found himself wondering whether everything he had given up so long ago might be possible after all.


	7. Chapter 6

**Notes for the Chapter:**

> I am ... really fascinated by where you guys think this story is going. Because in some ways, you're right. But in other ways ... well, you'll see. ;)
> 
> Thanks so much for your support, and I hope you enjoy the new chapter.

It was two in the afternoon, and his dad hadn’t said a single word since they got to the lab.

This might not have concerned him, if his dad had been in the midst of a project, or at least _appeared_ to be in the midst of a project. But he didn’t even put up the facade. He walked around, cleaning the dust off of things that must not have been touched since before Sans was born, scrubbing old test tubes and stacking piles of unsorted papers and even polishing the rusty file cabinet.

His dad was good at many, many things, but housework was definitely not his forte, any more than it was Sans’s.

That was probably why Papyrus had become such a neat freak in the first place.

Yet there he was. Cleaning. Just like he had spent the entire weekend cleaning the house from top to bottom—quite a feat, given that Papyrus usually kept it spotless. Sans had finally taken Papyrus out to Snowdin for a few hours just so he wouldn’t get any more worried than he already was.

Papyrus could be oblivious in some ways, but he was observant, and he knew their dad just as well as Sans did.

By Sunday evening, every spec of dirt had been banished from the house, and their dad had taken up cleaning out his old computer, deleting unneeded files and sorting the rest. When Sans woke up Monday morning, bright and early, he found his dad still staring at the screen, three empty cups of coffee on his desk while he propped his head up with one limp hand.

He came very, very close to insisting his dad stay home for the day.

But he had pulled far too many all-nighters himself over the years to have anything to say about his dad’s behavior. So he just sighed and made sure that both of them grabbed breakfast before they left the house.

He got to work, just as he had every day for the past three weeks.

And his dad … started cleaning.

For an hour. Then for two. Then for three and four and through his lunch break, the lunch break he had always _forced_ Sans to take, no matter how absorbed he was in his work.

When the clock on the wall struck 2:30, Sans stood up from his chair, turned to his dad—dusting the walls, at the moment—and let out a long, heavy sigh.

“It wasn't your fault, you know.”

His dad’s head snapped up so fast it almost threw him backwards, and it took him several seconds to identify the source of the noise and face Sans, his sockets wide.

“I'm sorry?”

“The experiment,” Sans replied, crossing his arms over his chest. “I agreed to it. I knew what the machine did, I knew it hadn’t been tested, I knew _exactly_ what I was getting into. And I know you set it up better than anyone else could.”

His dad stiffened, his mouth tightening into a thin line. He looked away. Sans sighed again.

“Things happen. Stuff goes wrong. I mean, you didn't blame Pap when he set the lab on fire.”

“He was four,” his dad murmured.

“Yeah, and he was seventeen when he burned down the kitchen. And I was _eighteen_ when I almost wrecked the M.I.A.O. machine ‘cause I didn’t read the manual first.” Sans’s face softened, just a bit. “Point is, I’m fine, and you did your best. No one ever expected anything more.”

He knew his dad’s worrying nature would never be placated by reassurance. He had guilt-tripped himself for weeks when Papyrus cracked his leg when he was seven, even though there was nothing he could have done to prevent it, short of wrapping both kids in bubble wrap. But usually Sans’s attempts at calming him at least did a bit of good. Sometimes it would prompt a deep discussion, or a hug, and they could go on with the rest of their day a little more peacefully.

His dad’s face pinched further, and he looked off to the side.

“That’s not what’s worrying me, Sans.”

Sans’s browbone furrowed. He took a slow, careful step forward.

“You didn’t do anything dangerous, did you?”

His dad’s head snapped back to him. “What?”

“You’ve got the same look on your face as you did when you switched some of the calculations around and almost blew up the Core.”

His dad blinked. Then his browbone rose, and he shook his head.

“No, no, nothing like that,” he murmured. He paused, and let out a soft, humorless chuckle. “Though … I suppose I can see how I would seem equally distressed.”

Sans took a step closer, but stopped there. He ran through everything that had happened over the past few days, searching for something, _anything,_ else that could have made his dad this upset.

“What’s up?” he asked at last, as casually as he could manage, even though he could barely keep the growing fear out of his voice.

His dad looked at him again, taking him in with such affection, such _pain,_ that it made Sans’s soul ache. It was one of the rare moments when he actually believed his dad was as old as he said he was, that he had really lived through all the horrors Sans had learned about in history class. Lived through them, and somehow still managed to smile.

Sometimes it wasn’t so hard to see how Papyrus could be his son.

After more than a minute, his dad sighed and turned away again.

“When I … attempted to repair your vision … you were connected to a machine to measure your vitals.”

“Yeah. I know,” Sans replied, slowly, his mind working overtime to sort out what the hell his dad was trying to say.

His dad shook his head and still refused to meet his eyes.

“The readings I found were … unusual,” he went on. He brought his hands close to his torso and wrung them, a nervous habit he had never been able to completely kick. “Not … unusual as might be expected during a stressful procedure, but … unusual … compared to other monsters’. Even after the procedure was complete and you had been fully healed.”

Sans just stared. His dad glanced at him, just for a second, his eyes soft despite his fidgeting.

“I believe I explained to both you and Papyrus the circumstances that led to your birth.”

Sans raised one half of his browbone. “You mean you getting bored on a Friday afternoon?”

His dad had always smiled when Sans brought up that fact. Now, his mouth didn’t even twitch. He shook his head. “Not just that. I wouldn’t have even thought of the experiment if I hadn’t had something … leftover from a prior experiment.”

“You said it was a nutrient fluid,” Sans replied, though with far less confidence.

“Essentially, yes. But it was a very unique nutrient fluid,” his dad said. He looked at Sans again, longer this time, and there was something in his eyes Sans didn't know how to read. His dad had only ever been a gentle, nurturing, slightly goofy father or an eccentric, scatterbrained scientist. This was neither. His dad let out another long breath and closed his eyes. “Along with a high concentration of magical energy, the same sort found in very nutrient-rich food … I included certain … essences, I suppose you could say, extracted from the human souls the king had collected.”

Sans stared. Then he stared some more. He stared with the firm belief that if he waited long enough, either what he had heard would start to make a bit more sense, or his dad would say something else. Neither occurred.

He swallowed.

“Wait, so … we were grown in human … stuff?”

His dad chuckled, with more fondness than amusement. “You never did like using technical terms, did you?”

“Not when non-technical terms do the job just as well,” Sans muttered. He glanced away, then back at his dad, then away again. He shook his head. “So … we’re …”

This time, there was no hesitation. His dad stepped forward and put both his hands on Sans’s shoulders, angling him so Sans had no choice but to meet his eyes.

“You are exactly what you have always been,” he said, his tone so sharp it would have sounded hard if not for the words it was forming. “My sons. Two very fine skeletons.”

Sans’s breath shook as he let it out, and his dad’s eyes softened, staring down at him in overwhelming affection. Then his hands fell, and he looked away once more.

“But your souls are … unique. _You_ are unique. You and your brother, I presume, since you were grown in the same substance,” he went on. “And the readings from your soul hold similarities both to monsters … and to humans.”

Neither of them moved. Sans wasn’t even sure if he was breathing. All the machines were turned off, so there wasn’t so much as a faint hum of background noise to make the lab feel less dead.

It was more than a minute later that Sans swallowed the thick lump in his throat and let his gaze drift down to the floor.

“Damn.”

When he glanced back up, it was to find his dad still staring off to the side, looking about a hundred years older than Sans knew he was. “Yes, I suppose that’s appropriate.”

Another pause. Sans swallowed harder, but the lump wouldn’t go away. He shifted to one foot, then to the other, as the cogs in his head began to turn, and the pieces of the puzzle clicked together, one by one.

“So … you think …”

His dad huffed again. His eyes remained shut, his head hanging in something like shame.

“I think further research into the … nature and behavior of your soul might lead to …”

“You think it could help break the barrier,” Sans finished as he trailed off.

His dad opened his eyes just enough to glance at him, one half of his browbone raised. “That’s quite a leap, Sans.”

“But it’s true, isn’t it?” Sans asked, even though he already knew, even though he didn’t _need_ to ask. “If we need human souls to break the barrier, and my soul is … more like that … I mean, there hasn’t been anyone like that before, has there? Someone with a soul like a monster _and_ a human?”

He could have cut the silence with a knife and served it up for breakfast. His dad averted his eyes.

“Not that I’m aware.”

A tiny bit of tension left Sans’s shoulders, even as he straightened as much as he could.

“Then this is what we’ve been waiting for,” he replied, taking a step forward, as if that would make his point any clearer than it already was. “I’m not stupid, Dad, I know you did research on that. How to synthesize human souls from material we’ve already got.”

“Yes, and nothing came of it,” his dad muttered.

“But it might now,” Sans shot back. His dad winced. Sans put his arms out to his sides, his whole body buzzing with energy he hadn’t felt since he first stepped into the lab. “So what are you waiting for? This could be our big breakthrough.”

“I can’t do that, Sans,” his dad muttered.

“Why not? This could get us out of here!”

“I’m not turning you into a test subject!” his dad snapped, jerking around to face him. Sans froze. His dad stared, both his eyes wide, his body stiff before his shoulders sagged again. He shook his head. “Sans … any kind of research I do would have to be on you. You or Papyrus—”

“We’re not using Papyrus,” Sans cut in.

“And I’m not using you either,” his dad finished. “Do you think the idea of you hurting is any easier for me than your brother hurting is for you? You’re my son, Sans, not some … thing to be studied.”

“But I _want_ to do this.”

His dad put a hand to his forehead. “These tests could be dangerous, Sans. I wouldn’t just be studying you while at rest. I’d be seeing how your soul responded to different situations and stimuli, some of them not exactly _pleasant._ ”

His teeth gritted so hard it must have hurt him. He ran the hand down over his face, then let it fall limp to his side as he shook his head one more time, more definitive than before.

“I won’t do that. I won’t hurt you. You and Papyrus are the most important things in the world to me, and I don’t care if we’re stuck down here for an eternity, _nothing_ would be worth harming you.”

Sans looked at him, just looked at him, his eyes wide and his smile tight.

“I’m one monster, Dad.”

His dad met his eyes again, mouth curved into a frown. “You. Are. My. _Son._ ”

“And I want to get out of here as much as the rest of us,” Sans replied. He straightened a little more as his mind began to clear. “Look, it’s not like this stuff would kill me, right? I’m not just your son anymore, I’m your _co-worker._ And I’m not helpless, either. You could tell me exactly what you’re doing, I could help, I could give real feedback. I could tell you if it got too bad. ”

“Yes, that worked out wonderfully last time,” his dad muttered.

“Dad, I’m _fine._ ” Sans’s hands curled into fists, even though he knew the mess of emotions swirling inside him was far from anger. At his dad, anyway. He breathed out hard and took a step forward,. “Please. This is our chance. And I’m the one who’d be doing the tests, anyway. Shouldn’t it be my choice?”

His dad tensed, but something shifted in his face. Something small, almost imperceptible, but enough to catch Sans’s attention.

“I want to do this,” he added. Another flinch. Another step forward. “If it could get us all of out of here … it’s worth whatever I have to go through.”

For a very long time, his dad said nothing, and this time, Sans let the silence fall. They both stood there, Sans watching his dad, his dad staring off to the side with a pinched face, every bone as tense as Sans had ever seen it.

When his shoulders fell at last, it was like the whole world had heaved the same sigh that slipped from between his dad’s teeth.

“Just one,” he said, like he was agreeing to let Sans jump head-first into a pool of lava. “We start with one, we see how it goes, and if it isn’t too bad, we can try another.”

Sans felt his smile widening by the second, his eyelights growing bright, his soul pulsing. His dad looked to him in full, his face blank, yet absolute.

“That’s the only way I’ll do this. And you have to tell me as soon as it gets too uncomfortable.”

Sans lifted two fingers to his forehead and swiped them down in a quick salute, but his skull-splitting grin probably killed the effect. His dad sighed and turned away, and immediately Sans bounded back to his work, his energy renewed.

Maybe he shouldn’t have been quite so excited to be a test subject.

But it was a way to contribute. A way to help the people around him. A way to actually make a difference, as he had so badly wanted to do for as long as he could remember. A difference far bigger than any he had ever imagined making.

A few uncomfortable experiments would be more than worth the potential result.

Neither he nor his dad said anything else for the rest of the day, but Sans barely noticed at all.


	8. -18.5

**Notes for the Chapter:**

> This chapter includes a few of my skeleton biology headcanons: first, that they are capable of basic movement, like walking, from birth, and second, that they eat solid food from birth. 
> 
> Unless you’re going with the “ecto-organs” theory, skeletons don’t exactly have the biology to be pregnant, so I assume that skeleton babies are grown externally (like Sans and Papyrus) or are “born” as young children. Being born as helpless as human babies is actually pretty strange: most other species are able to at least cling to their mothers, if not walk independently, from birth. The whole reason human babies are so underdeveloped is because their heads grow quite a bit faster than the rest of their body, and if their heads were any bigger at birth, well, they couldn’t be born.
> 
> As for solid food, skeletons also don’t have the biology to nurse their young, so there would be no way for baby skeletons to need milk as babies. So solid food it is! (Which also means no sucking reflex, i.e. bottles or pacifiers.) 
> 
> Oh, and the baby carrier mentioned in this chapter would probably look something like [this](http://assets.babycenter.com/ims/2015/04/Twingaroo_Twin_Infant_Carrier1.jpg).
> 
> Also, I apologize for any mistakes in ASL grammatical structure. I took ASL for a year in college, but it's been quite a while, and I was never an expert.
> 
> As always, thanks, everyone. Hope you enjoy. :)

The children were crying again.

Had they stopped? When had they stopped? He couldn't remember. Certainly they had stopped at some point, certainly there had been a moment of quiet sometime in the last—day? Week? Six months? There had to be. He just couldn't remember it.

All he could remember was the crying. The crying when he held them wrong, the crying if he forgot to feed them, the crying when they were under-stimulated or overstimulated, the crying if they got too tired and just _couldn’t get to sleep_ …

It had been worse when they were first born. Probably. He hadn’t known anything then, not what to feed them, how often they needed to eat, or sleep, or how to pick them up any other way than that awkward, uncomfortable position he had used to carry them home from the lab. He had gotten better since then. Probably. He had asked for advice, he had read books in the library—when he had time to _get_ to the library—he had learned from trial and error what worked and what just upset them more.

But now he had been trying everything he could think of for the past two hours, and they _wouldn’t stop crying._

He had put them in the carrier for half an hour, walking around the house, jogging around the house, even skipping around the house, stopping once or twice to just sway back and forth in place. He tried singing even though he couldn’t sing to save his life. He tried feeding them, putting them in new clothes, wrapping them in blankets, and just taking all their clothes off—they seemed to enjoy running around naked, maybe that would help. He had given them each and every toy that had been gifted to him since they were born, and he had made some of the most exaggerated, ridiculous faces he could think of. Nothing calmed them. They just kept crying.

Wasn’t it hurting them to cry this much? Should he heal them? Their HP seemed fine, but what if this kept going, what if it hurt them, what if he couldn’t get them to stop, what if they never stopped, he’d never be able to leave the house, he’d never be able to help them, they would be crying for the rest of their lives and he had failed as a father, it had only been six months and he had already managed to ruin everything—

A knock sounded at the door, and Gaster jerked around, ready to open it before he remembered that he had no free hands. He crossed the room to the couch and very gently and carefully laid the still-crying, squirming skeletons on the cushions, something deep within him aching at no longer having them in his arms. Then he scurried to open the door, his shoulders falling when he saw the monster standing on the other side.

Dr. Japer smiled at him from the porch, and instantly a small smile formed on his own mouth in return. He pulled the door open the rest of the way and offered her a path inside.

“Thank you for coming,” he said, on reflex. Dr. Japer just looked at him. He paused, then winced, lifting his hands and signing, more than a little embarrassed, HERE COME THANK-YOU.

She chuckled, but nodded, slipping past him with a faint gleam in her eyes at his likely-obvious blush.

“Of course.”

Gaster closed the door behind her and watched her cross the room with practiced ease, toward the couch and the two crying infants. He put a hand to his forehead, covering his eyes, and leaned against the wall.

It had only been six months that he had had someone to speak to that could actually understand him, and already he found himself speaking rather than signing to his colleagues several times a week. Six months, after centuries of silence, aside from muttering to himself. He would have thought it would take a lot longer. Had he really missed speaking that much?

He had been fortunate, all this time. Most monsters understood the basics of sign language—there were too many monsters who were nonverbal for various reasons to get by without it. But sign language had never been his natural language, as it was for some, and he supposed that somewhere deep within him, he had never lost his love for the spoken word.

Not to mention that making puns was infinitely more difficult in another language.

But despite his embarrassment, he was intent on having others over as regularly as possible. He didn’t want to risk the boys learning to mimic his font rather than fully expressing their own—rendering them just as incapable of communicating with the rest of the world as he was. As far as he knew, there had never been a skeleton who was raised hearing only _one_ adult font. Then again, there had never been a skeleton born from just _one_ skeleton in monster history, either, and yet two such young skeletons were right in front of him.

In Dr. Japer’s arms, at the moment, Papyrus reaching up to grab at her ears while Sans focused on a small patch of fur on her cheek. Their tears had already stopped, and if not for the faint marks on their cheekbones, Gaster would never have guessed they had been crying at all.

Silence had never sounded so perfect.

Dr. Japer had never smiled quite so wide.

At least, not since she had last come over a week before.

“So you finally found names for them, I heard?” she asked, though she didn’t take her eyes off the boys.

She turned to see him nod and lift his hands.

FINALLY START TALK. HEAR FONTS.

She hummed. “You know, one of these days you’re going to have to explain how that works. I’ve always been curious how skeletons hear that and no one else.”

Gaster didn't say anything. She had said the same thing at least a dozen times over the years. She was older than many monsters, but not old enough to remember any skeletons other than himself. The first time they had met, almost two centuries ago at the lab, all it had taken was a single spoken sentence to make her spend three days asking him questions about skeletons, about fonts, about _his_ font, which he answered mostly through writing, given that her sign language at the time was basic at best.

Some of his co-workers had told her to lay off him, but Gaster didn’t mind. There were hardly any books available about skeletons nowadays, and if he could make knowledge of his species survive in some way or another, he was happy to write a page—or twenty—of explanations.

He had waited for her to ask if she could try to learn his font. She never did.

He looked at her now, at the graying fur around her cheeks, the age and wisdom in her bright green eyes, and tried to figure out how the time had gone by so fast.

Was he really getting that old?

He turned his attention the boys again, now babbling instead of wailing. He would have taken the babbling for the rest of his life, nonstop, if it meant he never had to hear them cry. Dr. Japer bounced them every few seconds, adjusting them whenever they shifted too far one way or another, chuckling rather than wincing when Papyrus tugged a little too hard on her ear.

Gaster fidgeted again, his soul twisting in his chest.

HOW DO THAT? he signed, fiddling with his hands as soon as he finished. Dr. Japer tilted her head. Gaster made a vague gesture toward the boys, and he didn’t have to sign a word as his expression tilted from confusion to tired desperation. EVERYTHING TRY.

Dr. Japer looked at the boys, then back to Gaster. She smiled.

“When was the last time you were around kids? Before these two were born, anyway?”

Gaster stood up a little straighter. SEE EVERY DAY.

“I mean _interacting_ with them,” she went on. Gaster paused, then looked away. She laughed. When he glanced back at her, she was settling the boys on her hips, swaying back and forth. Both children snuggled into her sides. She gave Gaster another smile. “Well. If I’m going to be around here this often, I might as well give you a few lessons.”

Gaster just stared.

He showed her everything that he tried, and she told him what was a good idea, what was a bad idea, and what was incredibly stupid. Then she gave him some ideas of her own, little tricks that had works with her niece when she was first born. Balancing them on his arm while tilting them back. Humming to mimic white noise.

“Sometimes it’s just a new face that snaps them out of it,” she mentioned. “That’s probably why they stopped crying when I picked them up. They know me well enough that I’m familiar, but there’s still some novelty.”

She suggested a few things she had never tried before, but which she suspected—correctly—would work, given how the boys were created. Mimicking the sounds of a lab, clinking of glass, rustling of papers, feet tapping on tile floors: the sounds they would have heard during their prenatal development. Running a room-temperature bath and submerging them up to their necks, to mimic the feel of the nutrient fluid. Sans had begun to fuss again by the time she tried that one, and the second he was mostly underwater, he went silent, shifting his little limbs back and forth in the liquid, just like he had in the tube.

When Papyrus joined him, it took them less than two seconds to latch onto each other in the same embrace Gaster had caught them in so many mornings when he walked in.

But both of their favorites, by far, were head rubs, apparently a favorite of Dr. Japer’s niece. Gaster had never even considered it, and at first he wasn’t sure if someone with hands as thin and hard as his could do it. But a simple scalp massage calmed a squirming Papyrus as quickly as the bath had calmed Sans, and within a few minutes, he had curled up in Dr. Japer’s arms, perfectly still and already half-asleep.

In the meantime, Gaster slipped Sans back into his usual spot in the front of the carrier. He was close to sleep as well, and didn’t seem to mind being moved. Gaster tensed in fear that he would shift him too suddenly, despite his experience with the carrier—which he only had thanks to Dr. Japer picking it up at the Signa shop and giving it to him—but Sans just nestled closer once he was secure.

Papyrus remained in Dr. Japer’s arms. She shifted her weight from side to side, calming even his boundless energy with practiced ease. Gaster’s eyes shifted back to Sans, pressing his mouth into a thin line.

How was he ever supposed to do this? He couldn’t depend on Dr. Japer forever. This was meant to be his job. He had taken it on, after all. He had _chosen_ to take it on, he had _wanted_ to take it on. But he hadn’t truly considered everything he didn’t know, everything he would be so bad at, all the little challenges he would have no idea how to surmount.

Babies weren’t science experiments. They weren’t projects he could try out and shrug off if something failed. They were _alive._ No matter how they had come into being, they were just as alive and aware as any other monster. And every mistake he made meant they suffered even more.

It had been six months, and he hadn’t adjusted. Not really. Part of him still felt like this was going to end, that one day he was going to wake up and this would all be a dream and he would just go back to working in the lab all day like he had before, without two babies strapped to his back and chest.

Did that mean he didn’t really want them? He did want them. He knew he wanted them. But …

He wasn’t cut out for this. No matter what Dr. Japer taught him, no matter how much she helped, he just wasn’t cut out for parenthood.

Maybe he never would be.

“You’re doing wonderfully, you know.”

Gaster jerked his head up. Dr. Japer watched Papyrus as she ran her paw over his skull, rubbing tiny circles, just like she had shown him. He had never seen her eyes quite so soft.

“Even parents who spent years preparing for having kids usually feel like they have no idea what they’re doing when they actually have them. According to my brother, that never really goes away, no matter how old they get,” she went on. She turned to look at him, and a tiny smile tilted her lips. “I won’t say you’re the most competent parent I’ve ever seen, but they’re clearly very attached to you. And you to them.”

Gaster fidgeted with the hem of his sweater, then lifted his hands again.

LOVE THEM.

He couldn’t bring himself to look at her for almost a minute after that. His face must have been completely flushed by this point, and even though he respected her as an equal colleague, there was something about letting her see him quite this vulnerable that made it difficult to meet her eyes. When he finally did, she was smiling even wider, even more fondly, her gaze locked on him.

“I poke my head into your lab sometimes, you know,” she said. Gaster’s browbone furrowed. A mischievous, almost youthful glint flashed across her eyes. “You don’t really notice when someone opens the door if you’re focused on a project.”

Gaster tried to frown, but he had never been able to pull off the “strict professor” look she once accused him of attempting. Dr. Japer smiled a little wider, but said nothing, looking down at Papyrus, his eyes almost completely shut, and Sans, already fast asleep against Gaster’s chest.

“They’re always in their carrier. Even if you can barely work around them, you never leave them. And I’ve never seen you let them around anything dangerous.”

Gaster brought his hands closer to his torso, and one of them found its way to the top of Sans’s head. He still wasn’t sure he had mastered the motion Dr. Japer had taught him, but nonetheless, he ran his fingers over Sans’s tiny skull, then pressed a bit harder, massaging in small circles. Sans cuddled closer, and Gaster swore his permanent smile got just a bit wider.

“And I see the way you look at them,” Dr. Japer finished, so quietly she might have been talking to herself. He looked up. Papyrus had finally fallen asleep, and she cradled him with ease while her eyes remained on Gaster. Suddenly, he felt like the young recruit, and she looked like the wise, veteran scientist. “Anyone who looks at their children like that can’t be half as bad a parent as you seem to think you are.”

Gaster opened his mouth, ready to protest, but no words came out. Though he couldn’t let her words soak in, he couldn’t bring himself to deny them.

He looked down at Sans, then to Papyrus. The two precious little boys he had watched grow over the past six months—the past _ten_ months, really, ever since he first found them floating in the mason jar in his lab.

Just two shards of bone, and now they were stumbling around on their own legs, babbling, laughing, talking.

And they were his. His children.

“You see?”

Gaster glanced back up, just long enough to see Dr. Japer watching him with a gentle smile and equally gentle eyes. She shifted Papyrus away from her chest and held him out, and without thinking, Gaster took him in one arm and settled him close to his brother. Papyrus stirred, then settled back to sleep, his tiny body cradled against Gaster’s chest.

“Just remember that feeling,” Dr. Japer went on. “Remember how much you love them. Keep learning. Keep trying. You’ll get there.”

Gaster didn’t even look at her. He couldn’t bring himself to do anything but stare down at these two boys.

He still felt helpless. He still had no idea what he was going to do. Without a doubt, they would cry again, and Dr. Japer would come over and calm them and he would try and fail to imitate everything she did. Over and over.

But … they had already managed single words, and soon they would be speaking in sentences. They could tell him what they wanted, what they needed. And he would learn to communicate with them. To listen. To know what they wanted so they would never need to fall to crying to get it.

He would get to know them, not just as infants, not just as tiny skeletons whose existence was a marvel in itself, but as individuals. What they liked and disliked, what their interests were, how they would take after him and how they would be different. All the things he had wanted so desperately to find out before they were born. All the things that had ensured he could never give them up.

Dr. Japer’s hand rested on his shoulder and gave it a firm squeeze.

“As long as you’ve got that feeling, as long as you remember how much they mean to you, you can do this.”

His mouth twitched up at the corners. He held the boys a little tighter, feeling the warmth of their bones against his, the thrum of their souls so close to his own.

“Thank you, Dr. Japer,” he murmured.

As soon as he realized he hadn’t signed it, he looked up, expecting to see confusion, but instead, she just smiled, as gently and knowingly as before. She gave a small nod.

“Anytime.”

Gaster found himself smiling back, before looking down at Sans and Papyrus once again. They rested against his chest, motionless save for their quiet breathing, their tiny sockets shut, the bones of their face smooth and calm. Like they had all they could ever want. Like they belonged there.

Yes. These boys were everything to him. Everything he had hoped for. Everything he had wanted.

And no matter what challenges he faced, he was going to find a way to give them everything in return.


	9. Chapter 7

**Notes for the Chapter:**

> THANK YOU FOR THE [SUPER ADORABLE DRAWINGS](https://missccp.tumblr.com/post/162934188892/inspired-by-the-time-sans-first-wore-his-lab-coat), MISSCCP!! :D I love them, they're absolutely precious. Thank you so much!! Sorry that the new chapter isn't quite as happy as the drawings ... *COUGH*
> 
> Those violence warnings? They start here. Proceed with caution.

As eager as Sans was to get started—disturbingly so, in Gaster’s opinion—it took several days before the first experiment was ready to begin.

 Or, at least, that was what he told Sans. He had gotten more complicated experiments ready in a matter of hours. But that had been when he was a good deal younger.

And working on experiments he actually wanted to perform.

But Sans didn’t protest, and Gaster allowed himself the extra time not only to think through every aspect of the first test, but to brace himself for actually performing it.

He was really going to do this. He was really going to perform an experiment on his son.

Not a medical experiment, not something that could potentially _help_ him, whether or not it actually succeeded. But an experiment _meant_ to harm him, because that was what would garner the most useful results.

It didn’t really hit him until the morning of the experiment itself. He took longer eating breakfast, even though Sans was already gone by the time he woke up. Papyrus, oblivious to what he was going to do, patted him on the shoulder three times while he ate, offering him soft, encouraging smiles, the same he had given before particularly difficult days at work. He took the long way walking to the lab. He paused for a couple of minutes in front of the elevator door, just breathing, trying to find any way he could get out of this. During the whole elevator ride, he had to hold himself back from banging his skull against the wall.

He stepped out, trudging through the halls like a man walking to his death. He almost would have preferred it that way.

He would have taken all this suffering in a second if it meant his son would be spared it.

“Dr. Gaster?”

Gaster tensed, then turned around, far more surprised than his should have been to see the familiar furry face staring back at him from down the hall. He tried to smile, but he knew it came out shaky at best.

GOOD MORNING, DR. JAPER.

But Dr. Japer didn’t even try to smile back. She frowned more the longer she looked at him, and took a few steps forward, head tilted to the side.

“Is everything alright?” she asked. Gaster couldn’t quite hide the stiffening of his shoulders. Dr. Japer’s forehead creased. “You seem … upset. Is something wrong?”

He tried to say no, but his mouth wouldn’t even open, and it only took a few seconds of uncomfortable silence for Dr. Japer to get all the answer she needed.

“Is there anything I can help with?” she went on. He recognized that tone. How many times had he heard it, every time she came over when the boys were small? How many times had she tilted her head and known, just _known,_ by looking at him, that something was bothering him, even if he didn’t want to admit it?

His fingers clenched at his sides before he lifted his hands.

“Morning, Dr. Japes!”

Gaster paused, and Dr. Japer looked over his shoulder, breaking into a wide grin. “Oh, good morning, Sans!”

Sans was standing just outside of the lab door, waving, when Gaster turned to face him. He turned to Gaster, half his browbone raised in expectation.

“Dad, are you coming? We should be ready to start soon.”

Dr. Japer’s brow furrowed. “Start?”

“Oh, just a new experiment,” Sans replied, before Gaster could even begin to think of what to say. “Nothing that interesting, just some fiddling.”

Dr. Japer looked at Gaster, then back to Sans.

“Is that what’s got your father so worked up?”

Sans chuckled and shrugged, so casually it made a shudder run up Gaster’s spine. “Oh, probably. You know my dad, he puts his all into everything he does!”

“He certainly does,” Dr. Japer said, and Gaster couldn’t tell whether the fondness in her words quite outweighed the remaining concern. She turned to Gaster one more time, then nodded at Sans. “Well, let me know if you need any help.”

“Sure thing!” Sans called back, waving again as she turned and walked back down the hall. Gaster watched her go, his mouth pressed into a thin line, as if that was all he could do to keep himself from calling after her, telling her what they would be doing so she could talk Sans out of it.

Dr. Japer turned the corner, and Gaster said nothing.

“Dad?”

Gaster closed his eyes, letting himself pretend that his son was just calling him to chat, or help with dinner, or clean his office, or any number of ordinary things he would have taken over this.

Then he let out a long breath, turned, and walked the rest of the way into the lab.

Sans, of course, had already prepared almost everything in the time since he had arrived—not that Gaster had expected any different. He was almost surprised—though more than a little relieved—that he hadn’t lain down on the examination table already. But thankfully, he allowed Gaster a few more minutes to get the last things set up.

Not that there was much else to set up. The experiment required only the monitoring devices he already had on hand.

And him.

And Sans.

But still it, was only after he had checked the monitoring devices seven times that he finally turned to face his son.

Sans was watching him, his sockets wide and his eyelights bright with enthusiasm, like he had looked the first day on the job. Gaster felt a rush of nausea that had no definite source. Sans smiled wider.

“Ready to start?”

Hearing it was even worse. Gaster put a hand to his forehead, took a deep breath, then let his arm fall limp to his side.

“I doubt I ever will be,” he murmured. “But everything is prepared. You understand what we’ll be doing?”

“Perfectly,” Sans all but chirped.

“Go over it for me,” Gaster replied, holding his head up again. “Every single step.”

Sans smile slipped. “I’ve done that three times already.”

“Then once more won’t hurt you.” Sans stared back in distaste. Gaster sighed. His browbone tilted up, and his face softened. “Please, Sans.”

Sans’s irritation vanished as quickly as it had appeared. He straightened, even though his eyes kept drifting toward the examination table.

“You hook me up to all the monitors. Then you administer small amounts of physical damage, the same that would knock about 5 HP off most monsters. You see how much damage is actually done, then you measure how my soul responds and heals and compare it to the data you have on human souls.”

Gaster stared at him for a few seconds. Sans stared back. Gaster put a hand to his forehead and bit back a groan.

“Good gracious, this sounds worse every time we go over it.”

Sans huffed. “Dad, come on. This is the only way we can get this information.”

Gaster looked back up at him, looked at his _son,_ who he was about to hook up to a bunch of machines and experiment on for the sake of science. How had he let Sans convince him to go this far?

“We don’t even know if this will help us,” he replied.

Sans shrugged, so casually, so dismissively it made Gaster want to scream.

“Well, we have to start somewhere,” he said, and as much as it pained him, Gaster couldn’t find a single word to say in disagreement. Sans looked at him, this time with more sympathy, though his impatience still shone through. “Once we’ve got a few readings, we can figure out exactly how similar my soul is to a human’s. Then we at least know what we’re working with.”

What they would _do_ once they “knew what they were working with,” Gaster still had no idea, and he doubted Sans did either.

But no scientific discovery had ever happened because someone knew exactly what they were doing. The idea for the Core had popped into his head while he was taking a shower. His own sons had been born out of a brief moment of curiosity and boredom.

That didn’t make it any easier to nod and motion for Sans to lay down on the table.

It didn’t make his soul twist any less when Sans did so with a wide smile and a bounce in his step.

Sometimes he really wished his son hadn’t inherited his unhealthy love of science.

He came very close to asking, one more time, whether he was sure, but he had enough sense left to know it would be worthless, and would probably just irritate Sans. Even as Sans looked up at him with the same bright smile, the same eager eyes, Gaster could see a touch of anxiety he couldn’t quite hide. In a way, it relieved him. If Sans had felt no trepidation, Gaster probably would have questioned his mental health.

More than he already was, of course.

It took several minutes to hook all the machines up to Sans’s body, and several minutes more to get an accurate baseline from all of them—now that Gaster was actually in the state of mind to write _down_ that baseline. Sans remained still, oddly patient given his excitement, while Gaster watched the clock ticking by like the timer on a bomb, counting down until he would have no more excuses to wait just a little longer.

As he scribbled down the last number of the base readings, he looked over the experiment plan, neatly typed with only a small coffee stain near the corner. He must have read it over two dozen times in the past few days, but he glanced over it one more time, just to ensure he hadn’t forgotten anything. He hadn’t. It was just as simple, straightforward enough for a five-year-old to understand. And he was just as insane as he remembered.

Gaster looked at Sans. Sans smiled. Gaster wished, for a split second, that he could die then and there.

But, of course, he didn’t.

Life had never been that kind.

He summoned the first bone, and it was like ripping out a part of his own soul in the process, even though he must have summoned several million bones over the course of his life. It hovered above his palm, floating there, taunting him, and Gaster fought the urge to crush it and forget about this ridiculous idea once and for all. Sans looked at the bone. Then he looked at him.

He didn’t say anything. He didn’t need to.

He had said plenty already.

And Gaster knew there was no way for him to back out. Not now that Sans was invested. Not now that he would make sure, one way or another, that they saw this through.

He curled his hand into a fist, but managed not to crush the bone at the same time.

Then he stepped forward, lifting his hand just enough to command the bone up. Above the table. Above his son.

Sans flashed him a quick, nervous, yet proud smile, then shut his eyes.

Gaster bit back the whimper fighting its way up his throat.

And before he could tell himself how stupid all of this was, he commanded the bone down, slicing through the air and slamming into Sans’s ribcage.

Sans winced, his whole body tensing as his HP dropped 3 points. Gaster jerked back, then stumbled forward, ready to heal him, only stopping when Sans squinted up at him with a weak glare. Gaster paused. Sans shook his head. Gaster’s hands trembled in the air, then fell to the side.

Dragging his eyes to look at the readings was like pulling out his own teeth, but he managed it, running over the numbers like he was reading a foreign language. He picked up a pen with shaky hands and jotted down a few notes before setting it down and looking back to Sans. His face had smoothed out, the pain apparently subsiding, and it would have been so easy, so, _so_ easy, just to let him rest.

But the attacks were meant to be applied at forty-second intervals. And Gaster wouldn’t put it past Sans to make him do it one time extra if he waited too long.

He summoned another bone.

It hurt worse this time. He had never been sure if the feeling he described as nausea was anything like how others experienced it, but he had never had more empathy for monsters who could vomit.

Sans’s eyes were still shut. That didn’t make it easier when Gaster brought the bone down again.

It took nine hits before his HP got low enough that Gaster refused to go any further. But thankfully, they had agreed on this beforehand, and Sans didn’t protest when Gaster turned his attention back to the readings, marking down notes as Sans’s body began to heal on its own. He had never paid this much attention to his son’s healing before. He had been far more intent on making sure he _did_ heal. But …

… now that he watched carefully, it _was_ different from what he knew of other monsters. Even other skeletons, at least as well as he could remember, and certainly different than himself. It was faster, yes, but the method of healing was different, too. Other monsters relied entirely on their magic to heal them, and often needed the help of either food or other monsters to heal fully on their own. But Sans … he used his magic, certainly, but it was more like he was simply … _refusing_ his injuries. As if he refused to let himself remain hurt.

He got better by sheer force of will.

Gaster waited until his HP rose to 25 again. There was no way for him to wait for it to max out—though Sans apparently healed faster than average, it wasn’t instantaneous, and since Sans had insisted that Gaster shouldn’t offer his own healing for the duration of the experiment, he expected it would take hours for his HP to return to normal.

Part of him wanted to wait hours. Maybe it if he waited that long, Sans would change his mind. Or just pass out and not be able to continue until tomorrow.

But that would just mean more of this later.

And the sooner he could get this all over with … the sooner he would _never have to do this again …_

The bone appeared in his hand almost without his command, and through every hit, he told himself that soon, this would all be done. And both of them could just go home.

After the second round, he paused, staring down at Sans despite his best attempts not to. His face had scrunched up, his teeth gritted, his sockets shut so tight it was almost hard to tell them from the surrounding bone. But after a few seconds without attacks, without a sound, his sockets opened, eyelights flicking from side to side as his breath came in shivering huffs.

Gaster squeezed his hands into fists.

“You're in pain,” he murmured.

Sans let out a shaky breath through his teeth, but didn’t meet his eyes. “I’m okay.”

Gaster’s browbone lowered.

“'In pain' is not 'okay,' Sans.”

Sans glanced up at him. His eyelights were more blurred than usual, but he still managed to focus on his face before huffing and looking away again.

“Look, we knew this was gonna hurt, didn't we? Right from the start,” he muttered, though his discomfort slipped out in his tone. “I agreed to that. The whole point of this test was to see how my soul would react to it. It's only gonna hurt worse if we keep talking about it.”

Several seconds ticked by in silence. Gaster grit his teeth.

“We should stop.”

“We're not stopping,” Sans snapped, though it was barely louder than a whisper. He met Gaster’s eyes again, browbone creased, smile tight. “We agreed. Just keep going, I’ll tell you if it gets too bad.”

Gaster sincerely doubted that. Sans had once managed to explain the theory of relativity to a group of wide-eyed freshmen—and get them to _understand_ it—after three sleepless nights in a row. If there was one things Sans was good at other than academics, it was keeping things to himself if he thought there was a good reason.

Nevermind whether it was _actually_ a good reason.

Sans forced a smile, as strained as it looked, and Gaster gritted his teeth and stared at his feet.

Then he raised his hand and summoned another bone.

He was aware of very little after that. He heard Sans’s winces and grunts of pain. He heard his own attacks hitting, one by one, mashing down his son’s HP, though never below 10. Several times, Sans had to remind him to measure how long it was taking him to heal, to keep track of the readings on his soul as the attacks impacted and his HP lowered and rose back up. Gaster almost healed him on reflex at least ten times, but whenever he got close, Sans just stared at him, hard and unrelenting, and Gaster looked away and went back to the procedure.

He was never going to think of the word “procedure” the same again.

At last, they had gone through five cycles of injuries and healing, exactly the number they had planned out. And though Gaster feared that Sans would try to get him to continue, when he pulled back, vanishing the last of the summoned bones, Sans didn’t protest.

For half a minute, neither of them said a word. Then Sans tilted his head to face him, his eyes still half-lidded and blurred.

“So, what’d you find?” he croaked out.

He shifted as if to try to get up, but Gaster placed both hands on his shoulders and gently, carefully, held him down to the table.

“Rest first. Here, I’ll heal you.”

Sans grumbled even as Gaster gathered the magic in his hands and rested them over Sans’s chest, the closest he was willing to get to his soul at this point. “Dad, you need to get the rest of the readings down.”

“The readings aren’t important right now,” Gaster bit out, barely able to keep from snapping. He poured more of his magic into Sans, but Sans kept wriggling. Gaster sighed. “Stay still, let me at least get your HP back up a bit … I don’t know how you talked me into this …”

Sans didn’t say anything, and Gaster spent another minute pouring his own magic into his son. It didn’t take as long to get him back to full health as it had the first time, but then again, he had been more distressed then, more panicked, and that did no good for healing. When Sans’s HP returned to 40, Gaster pulled away, putting a hand to his forehead with another long breath.

“What’d you find, Dad?” Sans asked, pushing himself up now that Gaster no longer held him down.

Gaster hesitated. He hesitated for a very, very long time. And Sans kept looking at him, waiting for a response, waiting for him to say what he already must know to be true. Finally, Gaster sighed.

“It seems … our hypothesis is correct, at least in this respect,” he said, every word burning as it slipped past his teeth. He carefully avoided his son’s gaze. “Your soul sustained less damage than would be expected from attacks of that caliber. Not quite as little as a human, but … not as much as a monster’s, either. And your initial healing time and soul response follows a similar pattern. I’ll need to compare the exact numbers later, but …”

He trailed off. Sans was still looking at him, and Gaster didn’t need to turn to feel his smile widening, despite his lingering pain.

“We were right,” he said, quietly, reverently. Gaster tilted his head further away. Sans rested a hand on his arm, and Gaster couldn’t bring himself to pull back. “ _You_ were right.”

Gaster wanted to run from the room and hide in a corner and never come out. But he couldn’t move an inch.

Sans got off the table a few minutes later, when his legs seemed to be stable enough to hold him. Gaster tried to get him to lay down longer, to rest, he could just carry him home, but Sans refused, over and over, insisting that walking around would be good for his recovery. He eventually agreed to smooth a healing balm over the marks that had yet to fade, and even though the healing seemed to have stabilized his HP, Gaster still checked it at least once every minute, as if it might suddenly drop.

Though Sans ignored everything else he said, he did agree to go home a few hours earlier than usual. They wouldn’t be able to do any more work on this project for the rest of the day, and Sans seemed to agree that he wouldn’t be in the right mental state to do any of his own work until tomorrow. It was a small concession, but more than a small relief for Gaster, that Sans would be at home resting rather than running himself ragged here.

Besides, even if he couldn’t get Sans to rest, Papyrus had always been more skilled than him in that respect.

Even if he would have no idea why Sans needed rest in the first place.

“Are you coming?” Sans asked as he pulled his bag over his shoulder.

Gaster had been staring at the floor for the past minute, and even now, couldn’t bring himself to look at him fully. He shook his head.

“No, I … I’ll be just a minute. I’m going to clean things up here.”

Sans hesitated.

“Are you sure?” His foot tapped on the tile floor as he took a step toward Gaster. “I can hel—”

“No, no, you go on,” Gaster cut him off, as gently as he could. “I won’t be five minutes.”

Another pause, longer this time. Gaster glanced up long enough to see Sans’s browbone furrow.

“Okay,” he replied, resigned, still concerned. “I’ll tell Pap you won’t be long.”

Gaster nodded, a small, jerky movement. “Yes. Thank you.”

One more pause. Gaster didn’t look up to see Sans’s reaction, but a second later, he heard his feet tapping on the floor, slow and unsure but definitely moving away, toward the edge of the lab.

The door opened and shut. Sans’s footsteps faded down the hall, until they disappeared altogether.

A minute passed. Two. Three.

Then Gaster dropped to his knees so hard his bones almost cracked. He slid back until his shoulder blades touched the desk, his hands reaching up to press against his face and his head lowering until it rested on his knees. His breath hitched, and tears were pouring from his eyesockets before he noticed the first one fall.

In the silence of the empty lab, the image of his son’s pained face burned into his head, the two-thousand-year-old scientist curled into a ball and sobbed.


	10. Chapter 8

**Notes for the Chapter:**

> I'm gonna run out of ways to thank you guys very quickly at this rate. :)
> 
> That violence warning? Still very much in effect.

Gaster managed to put off the next experiment by five days.

He knew that there was no way to put it off forever. Sans had been insistent enough before, and now that they actually had _results,_ now that they had good reason to believe that further research would yield a significant benefit, there was no stopping him. And frankly, Gaster far preferred being in control of the experiments himself, rather than risking Sans trying to be both the researcher and the subject for his own studies.

Gaster wasn’t sure how that was possible, but this was Sans. If he wanted it badly enough, he would find a way.

He knew it was inevitable, but he had hoped, he had really, really hoped, that the next experiment would be something easy. Something relatively painless. He convinced Sans to do a few tests of his baseline vitals, even a quick endurance test, in the hopes of putting his mind on a different track. But Sans seemed intent on tests that would get the most telling results, and every single one he could think of involved some sort of pain.

Gaster had never really thought of Sans as a masochist, despite his tendency to run himself ragged getting things done.

But he seriously considered whether he might be wrong when Sans brought up the idea of electric shocks.

He hadn’t even realized at first where he had come up with the idea, and that had been the most worrying part. Did Sans _want_ to hurt himself? Was he just trying to think of ways to cause himself pain? Should Gaster get a psychologist to come talk to him? Only several hours later did he think to look into the file he had given Sans—the green folder, with the last human’s records. It had been decades since he had done those experiments. And the shock experiment had yielded just as little results as everything else. Looking back, he couldn’t even remember what purpose he had thought it would serve.

But the fact that it had been done at all, the fact that they had _readings_ on how a human reacted to varying levels of electric shock, was enough for Sans to think it would be a good idea to test how he reacted, too.

Sometimes Gaster wondered whether Sans forgot that half of his past experiments had been done on a whim.

There was no changing his mind once it was set on something, though, and eventually Gaster gave in. It was unusual, but it _would_ give them something to use to compare to the human’s readings—and even though there wasn’t exactly a baseline for how other skeletons reacted to electric shocks, Gaster had a general knowledge of electricity’s effect on monsters, and it would be a good measure of how much Sans’s general physiology, not just his soul, had been affected by the S.E.

That didn’t make it any easier to actually _do_ it.

“I can’t believe you talked me into this,” he muttered for the tenth time on Tuesday morning, avoiding Sans’s eyes as he put the final touches on the makeshift mechanism he and Sans had built together.

He didn’t have to turn around to feel Sans grinning. There really was something very wrong with that boy.

“Because you know I’m right,” Sans replied, his feet tapping on the tile floor, impatient. “We can learn a lot from this.”

Gaster didn’t say anything, and thankfully, Sans didn’t push him.

He had Sans check over the machine once it was finished—because frankly, he didn’t trust his own judgment after the last incident with something he had built. He didn’t really trust _Sans’s_ judgment either, given his apparent enthusiasm for risky experiments, but it was better than just him.

He looked away while Sans climbed onto the table and laid down, and he refused to meet his eyes the whole time he was hooking him up to the monitor and, finally, to the electric shock emitter. He didn’t want to do this. God, he didn’t want to do this, and it was only the beginning, there would be who _knew_ how many experiments after this before the research was complete. And he would have to perform every one. He would have to make his son suffer, over and over again.

And his son _wanted_ him to.

Gaster risked a single glance at Sans before he turned on the machine, if only to confirm that he was still alright, that he hadn’t changed his mind, that there wasn’t _any_ chance he could want to get off the table and leave the lab and go get ice cream instead.

Sans just smiled.

Gaster turned to the control pad, his soul twisting so sharply he thought it might split in two.

It should have been easier than the first experiment. It wasn’t his attacks this time, and while before he had had to keep himself concentrated enough to summon bones, this time, all he had to do was press a button and write down the results.

It wasn’t easier.

The shocks were mild at first—no worse than the joy buzzer that Gaster had found in the dump several decades back and pranked a few of his friends with. Sans flinched, perhaps a bit more than Gaster remembered other monsters flinching at similar stimuli, but at that level, it was almost impossible to tell a difference.

Which gave Sans all the more reason to insist that they continue.

Gaster still didn’t know what a lethal shock would be for a human. He hadn’t dared to get close during the original experiments—it wasn’t like there were any other humans readily available should he go too far. And he had insisted that he wouldn’t reach the same maximum voltage with Sans as he had during the experiments with the human.

But there was quite a range between “joy buzzer” and “maximum voltage.”

Sans held up valiantly—uncomfortably so. He never cried out. Tears never touched his eyes. Gaster came very close to _asking_ him to scream, to cry, to complain, to do more than just lay there with his fingers curled so tight his hands shook, his sockets squeezed shut and his teeth clenched as each electric shock coursed through his body, jolting him, knocking the breath from his ribcage.

But nothing more than a whimper ever left his throat.

Up and up, stronger and stronger, so strong Gaster swore that he could feel the electrical currents in the air. With every zap, he swore he couldn’t breathe, he felt like his soul had been ripped from his body, like he was dying until Sans settled back down and then he zapped him again and he was dying all over. Each time, he wrote down the readings immediately after the shock, and each time, his handwriting got worse, until even he could barely make it out.

But Sans had left the original file right next to his notepad, and it took only a glance to see how similar each one was.

Similar soul activity. Similar physical response. Differing vitals, but that was expected, you could never _really_ compare a human and a monster in that sense. But it was close.

Gaster wanted to rip up the entire folder into tiny little shreds.

At last, he wrote down the last reading, and flipped the power switch so hard he almost knocked it off the machine. He didn’t notice how hard his hands were trembling until he brought them close to his torso. His eyes locked on Sans as he lay there, waiting for the next shock, before he seemed to realize that the hum of the machine had faded. He squinted his eyesockets open, but didn’t move.

It took several minutes before Gaster’s hands stilled enough for him to remove the clamps from Sans’s body, tossing them aside. They clattered against the floor, but he paid them no mind. Sans stayed where he was for another minute after that, then gritted his teeth and pushed himself up on the table.

Gaster wanted to say something. He _should_ have said something. But he didn’t know what to say.

Sans swung his legs over the side of the table and dropped to the floor, wobbling when his feet hit the ground. Gaster reached out to him, but he steadied himself. He grabbed his shirt off the small table where he had laid it before the experiment began, pulling it over his head. He fumbled three times pulling on his lab coat, but finally managed it, messily, before forcing one leg forward in a vague attempt to walk away.

Every movement weak and limp. The boundless energy that had so characterized him in Gaster’s mind nowhere to be found.

“Sans,” Gaster said, his voice catching in his throat.

Sans waved him off, though it looked more like his hand was flopping from side to side than actually waving.

“just gonna go lay down for a minute ...”

“Sans, _stop._ ” Sans stopped, though he didn’t turn around. Gaster sighed and stepped toward him, pausing a few feet away. “We're discontinuing these experiments.”

Sans stiffened, spinning around so fast he wobbled again and had to take a moment to regain his balance.

“What?” he asked, his voice a little clearer, but still vaguely slurred. His browbone furrowed. “But we just got started ...”

Gaster grit his teeth and shook his head. Sans leaned a little too far to one side, and Gaster shot forward, putting both hands on his shoulders to steady him. His soul ached almost as much as it had after the first attempt to heal Sans’s eye.

“Look at you. This is the _second test_ and you're about to fall over!”

Sans shook his head. It lolled, and his sockets grew hazy with the motion, even as he kept his face as blank as possible. “I'll be fine, just need a little rest.”

“No,” Gaster said, without any room for argument. “I don't care how much of your blasted consent you give. I'm the researcher, and I refuse to continue this experiment.”

Sans looked at him, eyes wide. Gaster squeezed his shoulders.

“I can't keep hurting you, Sans.”

“You're not hurtin' me ...” Sans murmured, though with far less conviction than every time he had argued before.

Gaster sighed.

“Yes. I am. And it's the most painful thing I've ever done.”

Sans finally stopped trying to move, or even look away. He just stared back at Gaster with eyes that suddenly looked a bit more focused. Gaster let his hands fall from Sans’s shoulders with another long breath.

“This doesn't just hurt you, Sans,” he murmured, and he made no attempt to keep the deep sadness out of his voice. “You're my _son,_ do you think I _enjoy_ doing tests that cause you pain? The exact thing I've spent the last nineteen years trying to protect you from?”

No response. Sans’s eyes shifted, but he forced himself to look forward. Gaster shook his head.

“It's not worth it. Nothing we could learn from this research is worth it.”

Sans started to talk. Gaster could hear the beginnings of the first word leave his mouth. Then he paused, staring at Gaster while Gaster stared back. And the rest of the words died before they could leave his throat.

Neither of them said anything else. Gaster pushed the machines back into the corner, if only to give his hands something to do. He wrote down his final observations—with more than a little reluctance, and only because he suspected Sans would get on his back if he didn’t do it on his own. Then, with one long look at Sans, he started out of the lab. Sans followed without a word.

It was one of the longest walks home Gaster could remember since he moved to Hotland. Then again, he rarely walked this slow, and in the past, he had either walked home alone or spent much of the time chatting with whichever of his sons was with him. This time, neither of them spoke at all.

Gaster wasn’t sure he had ever been more relieved and more apprehensive, all at once, to see his house appear in the distance.

Sans walked a bit faster, and Gaster sped up his own pace to match. They climbed onto the porch, and Gaster pulled open the door before Sans could get the chance. Sans looked at him, just for a second, his face unreadable, before he stepped inside, and Gaster followed right behind him.

“We’re home, Pap!” Sans called out as soon as the door shut.

Footsteps sounded in the kitchen, just out of sight, and Gaster almost smiled as Papyrus stepped into view with his hands on his hips and his favorite frilly apron tied over his torso.

“Well, finally! Dinner was getting—”

He stopped. The crease in his browbone disappeared, and his arms fell limp to his sides. He stared for a moment, the tight line of his mouth softened in shock.

“Sans, what’s wrong?” he asked, his irritation replaced by concern.

Gaster flinched. Sans stiffened, just enough for Gaster to notice, but managed a smile. “What are you talking about, bro?”

Papyrus stepped closer. His browbone furrowed in intent focus and more than a little worry. His boots tapped on the floor as he walked across the living room, his sockets wider with every step.

“You look … something’s wrong with you. You look … tired, and …” He trailed off. He looked at Gaster, then at Sans, then back and forth between them several times more. At once, he looked infinitely young and far older than anyone Gaster had ever met. “What happened? Did you get hurt at the lab? Were you doing something dangerous again?”

Perhaps his tone was meant to scold, but it came out more soft and worried than anything. Gaster’s soul twisted and stung, and he gritted his teeth. His gaze fell to the floor.

If looking into his own son’s worried eyes made him so ashamed, there was no doubt that what he was doing had very firmly crossed the line.

He took a moment to settle his thoughts, then opened his mouth and lifted his head to speak.

“Alright, alright, you caught me.”

Gaster paused, frozen, just as Papyrus turned to face Sans. Sans held both his hands up in a gesture of surrender, his smile tilted into something Gaster didn’t quite know how to read.

“I stayed up last night planning out a new experiment,” Sans said with a vague sigh of defeat, letting his hands fall back to his sides with a shrug. “Probably didn’t sleep more than an hour in the end.”

Papyrus’s frown deepened. “But you looked alright this morning.”

It took Sans less than a second to hum and shrug again.

“Guess it finally caught up with me,” he replied. He paused, stepping forward and giving his brother a warmer, softer smile. “Sorry for worrying you, Pap. I’ll make sure and get to bed early tonight to make up for it, okay?”

Papyrus didn’t say anything for a few seconds. He looked Sans up and down one more time, before finally huffing and shaking his head in long-held, yet fond, exasperation.

“Ugh. Well, I suppose that’s all that can be done at this point,” he said, though there was no more than a touch of actual frustration in his voice. His eyes softened. “You need to take better care of yourself, Sans! Sometimes I wonder what either of you would do without me around to look after you.”

His gaze flicked to Gaster. Gaster flinched. If Papyrus noticed, he didn’t say anything about it. He just turned back toward the table, waving them forward with the wooden spoon still in his hand.

“Come on, dinner’s already cold!”

Sans’s shoulders slipped as soon as Papyrus looked away, but he still smiled, following his brother with his hands stuck in his pockets. “You can just pop it in the microwave, you know.”

“I hate using that thing!” Papyrus replied as he reached the kitchen and began sorting through the large serving dishes he had laid out on the counter. “I spent all this time on a nice, fresh meal, cooked to perfection, and that box makes it taste funny!”

Despite the tension in his chest, Gaster couldn’t help a small smile. “Come now, Papyrus, you know any changes it makes are _micro-_ scopic.”

Papyrus paused, browbone furrowed, then groaned.

“Dad! I am not in the mood! And that was even worse than usual!”

Sans looked over his shoulder toward Gaster, flashing him a pleased smirk, and at last, Gaster followed his two sons into the kitchen.

Dinner was as normal as it had ever been—even though Gaster had long suspected that their version of “normal” was far from everyone else’s. Papyrus reheated the entire meal on the stove, and with all three of them in the kitchen, half the dishes ended up spilled. Sans picked up a spoon and ate the top layer off the casserole that had fallen on the floor, while Papyrus shouted about poor sanitation. Gaster made a frozen dinner, and Papyrus, exasperated, ate an entire serving dish of mashed potatoes, given that it was the only part of his cooking that had survived completely unscathed.

Sans started a food fight with the remaining casserole on the floor, and by the time they were done eating, the entire kitchen—as well as all three of them—were completely covered in mushy food.

They were all smiling, and Gaster wouldn’t have traded it for the world.

It took them half an hour to clean both the dishes and the kitchen, and even then, Gaster was fairly sure there were bits of casserole hiding in the crevices. He didn’t care, and even though Papyrus fussed, he never stopped smiling. It would have been so, so easy to forget about what had happened today, and go on without another mention of it.

But Gaster couldn’t let that happen. And apparently, neither could Sans.

They waited until after Papyrus had gone to bed—which, despite his energy level, was usually earlier than either of them, as he had always seemed to prefer what he referred to as a “healthier” sleeping pattern. When Gaster walked into the living room, he found Sans standing in front of the couch, staring at the wall. Gaster waited, unmoving, unspeaking, and eventually, Sans turned to look at him.

Seconds passed. Then minutes. Sans seemed to be waiting for Gaster to speak, but Gaster had nothing to say. At last, Sans let out a soft breath, the hard line of his shoulders falling when Gaster hadn’t even realized it had tensed up.

“Look. I don’t want him to know, okay?” he said, with a tone somewhere between exasperated and defeated. Gaster just stared. Sans sighed again. “If he hears what happened, he’ll think you hurt me on purpose.”

Gaster grit his teeth. “I _did_ hurt you on purpose.”

“Yeah, because we both agreed to it _as part of the experiment._ ”

Gaster looked away and brought his arms close to his torso.

“That doesn’t make it any better,” he murmured.

“Oh yeah?” Sans snapped, jerking Gaster’s attention back to him. “So it wouldn’t have been any worse if I’d been kicking and screaming the whole time and you did it anyway, huh?”

Gaster tensed. Sans’s hard gaze lasted less than two seconds before it softened again and his shoulders fell.

“Look, I’m fine,” he said. “I’ll _be_ fine. I just need a couple of days to rest and then I’ll be ready to keep going.”

Gaster’s mouth must have almost disappeared from how hard he pressed his teeth together. His arms curled against his chest. Sans kept looking at him.

“We got some good information from this one, didn’t we?” he asked.

It took all Gaster had not to look away again. If his arms pressed to his chest any tighter, they were going to get stuck in his ribcage.

“We’ve established a fair baseline, and if things continue as … expected … soon we should be able to begin exploring options for … strengthening a soul to survive without a body.”

“And after that, we start work on synthetic souls. And once we figure that out …” Sans’s eyes lit up like they had before the first experiment, his smile curling into something that reminded Gaster so much of the little nine-year-old who had blown all his classmates away at the science fair, but had been far too excited about his own work to care about winning first prize. “We’re already making progress. I’m more than happy to go through a few more experiments if it gets us this far.”

Gaster wrung his hands.

“It will likely be more than a ‘few’ more, Sans.”

“I know,” Sans said, as certain as he had ever been. “I don't care.”

Gaster sighed. Sans had a point, of course, he _knew_ he had a point. With everything they could learn from this, there was no telling how far they could go. They could get close to breaking the barrier. Maybe they really _could_ break the barrier. And if his sons could see the sun as he had so wished they could, even if he never dared to dream for it … if Papyrus could ride in a car, if Sans could see the stars he had given up on so long ago …

He didn’t notice Sans moving until he had already crossed the room, to the closet near the front door. He watched, silent, as Sans opened it and rummaged around inside, searching for something apparently hidden near the back. After a minute, he emerged, holding a large piece of white cloth.

It took several seconds for Gaster to recognize it as his lab coat.

He never wore his lab coat anymore. The only time he had worn it since the completion of the Core was for potentially messy or dangerous experiments, and those were few and far between. He couldn’t even remember the last time he had washed it.

He certainly couldn’t remember the last time he had worn it just for the sake of wearing it.

But Sans held it out to him with the same pride with which he had held his own lab coat on the day of his graduation. He offered it to Gaster, smiling in something like hope. Gaster’s hand reached out, almost on reflex, before he pulled it back.

“This is about your wellbeing,” he said, because he had to say it, one more time, he had to make sure Sans _knew._

Sans smiled a little more, as if he could see the resolve Gaster had once held so firmly beginning to slip.

“And I know you’ll be careful with it.”

Gaster opened his mouth. He paused, looking at Sans, waiting for the words to come to him, waiting for the protests to fall past his teeth.

Nothing came.

Gaster closed his mouth, and very slowly, reached out to take the lab coat in his own careful hands. Sans’s smile softened into something like relief.

Neither of them said anything else the rest of the evening, and though it took Gaster almost two hours to fall asleep, once his eyes finally shut, he slept through the night.

And his lab coat lay on top of the rest of his clothes on the foot of the bed, ready for the next day.


	11. Chapter 9

**Notes for the Chapter:**

> I can't say for sure whether it's the _worst_ you'll see in this story, but ... this chapter's content is one of the closest to torture I have planned in this little tale. So ... proceed with caution.
> 
> And as always, thank you for all your support. :)

Sans was used to losing track of time.

He was, as his dad had once said, a “passionate person,” even if Sans wouldn’t have described himself with those exact words. When he got into something, he forgot everything else around him, to the point that he once went two days straight without eating or sleeping and only noticed when he collapsed. That was normal.

This … was different, and yet it felt almost exactly the same.

It wasn’t actually him _doing_ anything. It was just him lying there, being poked and prodded and injured and healed, over and over again, while his dad took notes. The only thing Sans ever did was encourage his dad to continue. Though over what the calendar told him was more than two full weeks, even that had grown less and less necessary.

He wouldn’t say his dad had gotten used to it. But … it had gotten easier for him, just as Sans had adjusted to the regular doses of pain. He didn’t wince quite as much every time Sans winced. He didn’t spend ten minutes straight apologizing after every experiment. Sans didn’t have to remind him to get all his notes written down immediately, before time and his own emotional state diluted his memory—though even so, when Sans glanced over the reports, he found far more references to the “pain and distress of the subject” than was scientifically reasonable.    

He would really have to make sure and edit those before anyone else read them. Otherwise people really _were_ going to think his dad was experimenting on an unwilling subject.

But not today. Today, he was going to need every ounce of his attention to make sure his dad didn’t call off the experiment they had spent the past three days planning out to a T.

Everything was already set up. Sans had spent half an hour getting it all together when they first arrived, and his dad had spent almost two hours after that checking all of their notes, all of their procedures, and every single piece of equipment to be sure it functioned perfectly—though the actual equipment needed was exceedingly simple. And from what Sans could tell, everything was set up perfectly, and his dad should have been sure of that after only half an hour. But he humored him.

At least, at first.

After everything had been checked five times and he was still fidgeting and pacing and grinding his teeth, Sans felt his patience finally beginning to thin.

“Sans, are you sure you want to go through with this?” his dad asked—again, just as anxiously as the first time. “You can change your mind. You don't have to do this.”

Sans looked at him, just looked at him, hoping that a single look would convey everything he wanted to say, and everything he had said at least fifty times before. His dad just stared back. Sans bit back a sigh and nodded.

“It's important. We need to find out if souls like mine can survive, even briefly, separated from a body, and … this is the first step to finding out.”

His dad remained silent for a few seconds, staring at him with eyes Sans tried very hard to read, though he couldn’t seem to manage it. Slowly, his mouth tightened into a thin line.

“I'll give you a mild anesthetic.”

Sans huffed.

“Dad, you don't need to—”

“I won't argue on this aspect, Sans,” his dad snapped, more forceful than he had sounded in years. Sans tensed. His dad gritted his teeth, then sighed and looked away. “A … full anesthetic would likely interfere with the results, but a partial anesthetic shouldn't change much.”

He looked back out of the corner of his eye, though his head still faced the wall.

“This is going to be painful, Sans. Even with the anesthetic.”

“I know,” Sans said, completely deadpan. “You've said it twenty times now.”

“I'm still not sure it's gotten through your skull,” his dad replied.

Sans put a hand to his forehead and ran it over his face, then crossed his arms over his chest.

“I _am_ a scientist, you know. and I’m not stupid. I know that someone cutting into my soul is gonna _hurt._ ”

“Knowing that something is going to hurt and understanding it are two entirely different things,” his dad muttered, his gaze falling to the floor before snapping back up. “Trust me on that.”

Sans didn’t say anything. He couldn’t. There were things he would never know about his dad’s past. Things his dad didn’t want him to know, and things Sans never dared to ask.

But he had learned enough about the war in school to have a good idea.

He went silent for a minute, then caught his dad’s eyes again, giving him what he hoped came off as a reassuring smile.

“I’ll be okay, Dad. Pain isn’t gonna kill me.”

Again, his dad looked at him. Just looked at him, taking him in, too many thoughts running through his head for Sans to even begin to read them.

“If it gets too bad, I’ll stop,” he said. It wasn’t a question, or a suggestion, or anything other than a plain, nonnegotiable statement. “You tell me the _second_ it gets too painful, and I will stop. You understand?”

“Clearly,” Sans replied, half his browbone slightly raised, his smile somehow amused and exasperated all at once. “Just as clearly as the last fifty times you’ve said it.”

His dad let out a long, heavy sigh, but he said nothing else, and Sans supposed that was the best he could hope for.

He lay down on the table without another word, and kept as still as possible while his dad strapped him in. The straps had been Sans’s idea, and though his dad had protested avidly when he first brought it up, just as he had the first time weeks before, this time, he relented. It would be flat-out dangerous to risk Sans thrashing about and falling off the table, or making the procedure any more dangerous than it already was.

It was consensual, without a doubt, but Sans still found himself flinching with each strap that tightened around his limbs, locking him in place, and suddenly he understood why this idea had made his dad so uncomfortable.

He closed his eyes and took a deep breath.

This was fine. He was going to be fine.

This was going to hurt like hell, but he was going to be fine.

His dad paused once all the straps were in place and the machines hooked up to his body. He opened his mouth, the question so clear Sans could already hear it. Sans glared. His dad paused, then shut his mouth and went to find a syringe and the bottle of clear fluid that had probably been sitting in one of the closets since before Sans was born.

Anesthetics—or anything with a needle, really—were far more difficult to administer to skeletons, from what Sans had learned in his brief study of monster biology in college. Mainly due to the whole _made entirely of bone_ thing. Which was probably why they so rarely used them, even when in pain. His professor hadn’t planned on bringing it up during their segment on medical treatments and procedures, but Sans had never let a topic go by without asking some kind of question that threw the teacher off-course, and even though his family were the only remaining skeletons in the Underground, he wasn’t about to let anyone forget about them.

But Dr. Zelworth had been fond of him, and when he couldn’t find any books on skeletons that had been updated in the last two hundred years, he had brought Sans’s dad in to give the class a guest lecture—or, rather, to type up a guest lecture, which Sans then translated for the class.

That had been five years ago, but thanks to Sans, there was now a special class in the biology curriculum dedicated entirely to skeletons.

And Sans forced himself to focus on that memory rather than the sharp, grating sting when his dad maneuvered the needle in between the bones connecting his arm to his shoulder, stabbing into a bit of softer bone before pushing down the plunger.

It wouldn’t be very effective, Sans knew. But there was no other suitable bone close by, and no one had ever tested the effects of anesthetic directly on a soul.

Granted, to the best of Sans’s knowledge, no one had ever tried slicing into a soul before, either.

But hey, they were scientists. And there was a first time for everything.

It took a few minutes for the anesthetic to kick in, and Sans felt his senses begin to dull. Not very much, but more than he had felt before. He wasn’t sure if it was meant to make him calmer. He couldn’t tell whether it did.

His dad paused a very, very long time after that, and at first, Sans thought he was just waiting to make sure that the anesthetic was working. But after a few minutes had passed in silence, Sans looked up to find his dad wringing his hands and shifting his eyes from side to side. Sans bit back a sigh.

They weren’t backing out now. It didn’t matter how tense Sans’s body felt, how fast his mind raced, how hard his soul squeezed in anticipation of the pain to come.

They were going to do this.

“Dad,” he said, snapping his dad’s attention back to him. For a second, Sans could see every bit of the pain he had been holding back. All the hesitation. All the fear.

All the love.

And for a moment, Sans wanted to tell him to take off the straps and end this whole thing, once and for all.

But before he could get out a word, his dad held out his hand, curling his magic around Sans’s soul to pull it through his ribcage and out into the open air.

Sans gritted his teeth and curled his hands into fists.

Fine. He was fine.

His dad didn’t meet his eyes. Maybe he couldn’t bear to at this point. He reached for the tray four times before he actually managed to pick up the scalpel. His hand was trembling, and he spent another minute forcing it to still before he dared turn to face Sans again.

He glanced at him for half a second, then returned his gaze to his soul, as if staring at the soul rather than his face would make it easier. Maybe it did. Sans wouldn’t know. Even if it was useless, even if his dad couldn’t see it, Sans still gave a small nod, and a few seconds later, his dad reached out with his free hand and held Sans’s soul gently, carefully, in place. It … didn’t hurt, and Sans was torn between calling it comfortable and uncomfortable. Maybe both. It was his dad, warm and familiar and soothing, yet at the same time, Sans couldn’t ignore what he was about to do.

This was it. No going back now.

They had to do this. They had to know.

There was no other way.

As his dad slowly brought the knife down, Sans gave in and shut his eyes.

They had always said that pain wasn’t as bad when you didn’t see what was causing it. And no matter how determined he was to go through with it, he … wasn’t particularly looking forward to the process.

His dad must have paused—hesitating again, dammit, dad, that’s not helping anything—because Sans just lay there for what must have been more than a minute, gritting his teeth and waiting.

Then the blade touched his soul.

And it took every ounce of self-control Sans had had in his entire life not to scream.

He couldn’t breathe, he couldn’t think, his body tensed and he curled his fingers and toes and _god,_ why had he agreed to this, he could feel every microscopic movement of the knife, the imperfections in the blade, his head spun and everything was light and dark and he was going to die, _this_ was what it felt like to die.

The knife paused, and Sans heard himself say something, how was he speaking, _why_ was he speaking, what was he saying? Whatever had come out of his mouth, a few seconds later, the knife moved again, slicing down, down, further, further, it was never gonna end, he was gonna be stuck here forever, nothing but pain, agony, _what the hell were they doing what was this supposed to accomplish damn it all nothing was worth this it was awful it was—_

Then the knife was gone.

Sans breathed out, trembling and shaky, his throat tight and nauseous and for a second he thought he might actually throw up even though he didn’t have a stomach to throw up _with._

The pain faded from an overwhelming sting to a deep ache, his whole body as sore as if he had run a triple marathon. He didn’t think he could move if he wanted to, and he _really_ didn’t want to. And … there was something wrong. Like a part of him was missing. He still had all his limbs, right? What had the experiment been again? His limbs came off sometimes, sure, he was a skeleton, it didn’t hurt or anything, but this didn’t feel like that.

He twitched all his fingers and toes and searched his body for what was missing. But he couldn’t find it. It was … it was important, it was essential, and it was missing, not all of it, _part_ of it was …

With every bit of strength he could muster, Sans opened his eyes.

At first, everything was a blur of white. Bright lights, faint colors off to the side. Then his vision focused, bit by bit, and he shifted his gaze to the right.

There was … a person. A tall person. Papyrus? No, Papyrus wasn’t here, this was the lab, wasn’t it, Papyrus wouldn’t be here, so it was … his dad. Right. They were doing an experiment. On him. They had _finished_ the experiment on him. And his dad … his dad was …

He wasn’t looking at him.

Didn’t he usually look at him after an experiment was finished?

Instead, he was looking at a small glass container. The same one they had set aside before the experiment. Except it had been empty then, and this one … there was something inside it. A tiny sliver of something white.

Something … glowing.

Something that really, _really_ didn’t feel like it should be floating there, in that glass container, on its own. Separate. Separate from …

… him.

His dad’s hands fluttered a few inches away from it as he peered close, his sockets wide, his eyelights gleaming almost as bright as the fragment itself.

“It … isn’t vanishing …” he murmured. His browbone rose, his mouth tilting up into a wide, incredulous grin. “It’s still there.”

He glanced at his wrist as if there should be a watch there, but when he found no watch he turned to the clock, squinting to see it from across the room.

“Twenty seconds. Twenty-five … thirty … slightly unstable, but it’s still holding on …”

He looked back and forth between the fragment and the clock, his smile widening every time, his eyes so bright now they probably could have lit up a pitch black room.

“It’s incredible, Sans, just look at it!”

Sans shifted on the table, his vision sharper now even as his sockets tried to close. He could barely breathe for the ache in his chest, like he had broken all his bones, put them back together, then broken them again. He started to speak, but the words died in his throat as he looked at his dad’s face.

His eyes wide, the lights in them large and bright, the smile on his face more excited than Sans had seen it in years.

“Just look at it,” his dad breathed, his eyes locked on the glass container as he snatched up the closest piece of paper and pen and began scratching out notes. “It’s a little shaky, but it’s maintained its form, it doesn’t show any signs of disintegrating … hard to tell whether it’s the same shape, approximate edges seem intact … incredible … ninety seconds!”

His murmurs grew incomprehensible after that—or maybe it was just the haze in Sans’s mind. The pain came in waves, overwhelming him, suffocating him, letting him go just in time for him to force himself awake, as easy and tempting as it would have been to fall asleep.

He couldn’t look away. He couldn’t close his eyes. He couldn’t do anything but stare as his dad focused all his attention on the container in front of him, even more gleeful than he had been on the day he had finished the Core.

The soul fragment persisted for eight minutes and twenty-three seconds before shattering into dust, which his dad swept up into a test tube to be studied later. For twenty minutes after that, he scurried around the lab, marking down his notes, examining the readings each of the machines had taken, and writing the outline of a full report of the experiment, muttering to himself about the next steps to be taken.

And all the while, Sans lay on the table, biting back his groans and whimpers, watching his dad through blurred eyes as he bustled around the room, as if he had forgotten there was someone else with him at all.


	12. Chapter 10

**Notes for the Chapter:**

> I have to say, it's ... quite interesting to see where all of you think this is going. I mean, we all know it's not going anywhere nice, but as for how we get there ... ;)

Over the next week, they did three more soul-cutting experiments.

The fragments taken weren’t quite as large as the first, and they were always spread two days apart, to minimize the risk of serious damage, and to allow Sans’s soul time to heal and regrow. On the days off, Sans went to the lab in the mornings only to collapse on the raggedy old couch his dad had dragged in from the breakroom, sleeping for hours at a time even though he had already slept through the entire night.

It never seemed to do any good. He still had to grab the couch to keep from collapsing whenever he stood, and his body never ached any less.

And every time he woke up, it was to his dad bustling around the lab, taking notes, rolling out old machines, examining data and writing up reports.

And, of course, planning the next day’s experiment.

In the haze of half-sleep, Sans sometimes thought that he was four years old again, taking a nap in his and Papyrus’s playpen while his dad was working. Opening his eyes just enough to catch a peak of the man in the white lab coat, muttering nonsense to himself, shoes shuffling against the floor, the whole room filled with the clinking of test tubes and the buzz of half a dozen machines.

His dad, the Royal Scientist.

Funny, how that lab coat made him look so different.

He was there when Sans arrived in the morning, and he often stayed after Sans left, lingering in the evenings working on who-knows-what. Sans wasn’t keeping track anymore. He didn’t have the energy to do anything but drag himself to the lab and lay down, either on the couch or the examination table. He didn’t pay attention to the results. He didn’t read the reports. All he knew about the experiments that were being performed on him was what he could feel, as well as his dad’s occasional murmurs that slipped through the fog in his head.

Today had been easier—by a small margin. Rather than cutting a piece off of Sans’s soul, his dad just poked into it with the scalpel in a few different places, to test the rates of healing nearer and further away from the areas that had already been cut. The experiment had finished up around noon, and by five, Sans managed to get off the couch and walk across the room without collapsing halfway there.

He glanced over his shoulder when he reached the door. His dad still stood by the desk, sorting through old notes and marking down new ones. Maybe he had been doing that for the past five hours. Sans couldn’t remember, and frankly, he didn’t care.

His dad didn’t hear him slip past the door and into the hall.

Sans could always tell when he left whether his dad would be coming home to eat dinner with them. There was no point in asking.

It was long, long walk home. It hadn’t seemed long at all when he first started working at the lab, but now it felt like trekking across the entire Underground. Barefoot. On rusty nails. The pain had faded, but his energy hadn’t returned, and every movement was a new struggle. He swore someone had strapped invisible anvils to his feet. For all he knew, his dad had. It wasn’t like he had been conscious enough to notice.

He passed by other people, he was sure. He always did. At least half of the Underground got off work around this time. But he didn’t notice them, and he didn’t speak to them. The last time he had even interacted with someone else was two days ago, when Dr. Frewth found him collapsed near the lab door, trying to get his key card to work before he remembered that the door was automatic from the inside. Dr. Frewth had asked him about fifty questions and insisted on helping him get home, but Sans had brushed him off, and eventually, Dr. Frewth relented and let him be.

Today, there was no one. So Sans just kept walking, keeping his mind on his house, the image so clear in his head that when he finally saw it, it took him several seconds to realize it was real.

The sigh that slipped past his teeth took nearly all his tension with it.

He swore it took him less than ten seconds to make it the last ten yards.

He pushed open the door as quietly as possible, even though he knew it was useless. As soon as he got a good view of the inside of the house, Papyrus had already turned to face him, standing in the back of the living room, next to the kitchen table. He had already taken off his oven mitts, but he still wore his favorite frilly apron, the one he had seen in the store when he was fourteen and their dad had bought him without a second thought.

Sans was well aware his smile wasn’t half as convincing as it should have been.

“Hey, bro.”

Papyrus just looked at him. He wasn’t smiling, and it made Sans’s chest ache twice as much. He imagined that smile sometimes, in the worst moments. Imagined his brother’s bright, eager grin greeting him when he got home.

Had he been smiling when Sans got home yesterday? The day before?

Had Sans not noticed?

“I wasn’t sure if you were coming home,” Papyrus said at last. He wrung his hands and looked down at the table in front of him, set with three full plates. “I made enough for all of us.”

Sans’s shoulders fell, and he had to use all his willpower to keep his head from falling, too. “sorry … just you and me this time.”

“Oh.” Papyrus stared at the table again. He rubbed one of his hands with the other before finally picking up one of the plates, the one sitting in front of the seat neither of them had claimed for as long as Sans could remember. “Well … I’ll go put this back in the fridge, then. No sense letting good food go to waste.”

Sans stood there, silent, as Papyrus strode away, back into the kitchen.

His brother knew something was wrong. There was no doubt about that. His HP was lower than usual, and there was no hiding that from Papyrus. He was usually average for a monster his age who didn’t spend much time training to fight—far lower than Papyrus’s, without a doubt, but that had never bothered him, and he had never striven to make it higher. But even though he hadn’t checked the exact number in a couple of days, he could feel it in his bones, in every step he took, in every breath, in every shift of his eyes.

And if there was one thing Papyrus kept track of, it was the wellbeing of those around him.

But he hadn’t said anything about it yet, and Sans was all too willing to skirt around the topic for as long as he could.

Papyrus returned, and they both sat down at the table to eat the partially-cooled meal. Sans didn’t pay attention to what he was eating until he had taken a few bites, but he found himself appreciating the taste nonetheless, just warm enough, with a perfect blend of spices, the vegetables—he glanced down to confirm they _were,_ in fact, vegetables—just crunchy enough while still soaking up the sauce and softening up to be easily chewed.

“This is really good, Pap,” Sans said, after more than five minutes had passed without any sound but the clinking of utensils against dishes. He tried to smile, though it came out barely wider than his usual permanent grin. “You always were the best cook.”

“Only because Dad taught me,” Papyrus replied, without looking up from his food.

Sans gripped his fork tighter and scooped up another bite of vegetables. “hm.”

Silence again. Sans took another few bites of his dinner, trying to figure out all the spices Papyrus had added to it. He liked to go a little crazy with the spice combinations, and they had been barely short of overwhelming when he first learned to cook. But their dad had been patient with him, explaining how to best gauge which spices went well together and how much to add, and now Sans had little doubt Papyrus could work at a restaurant if he wanted to.

“It’s been three years.”

Sans’s head snapped up. Papyrus was still staring at his plate, motionless. Sans might have assumed he had imagined it if not for the tiny, pained crease on his brother’s browbone.

“What?” he managed.

“It’s been three years since he missed dinner with us,” Papyrus said, his voice quiet, his face blank. “He’s missed dinner four times this week.”

Sans winced and bit back a curse that made its way up his throat. He glanced at the door, even though he knew it wouldn’t open, and probably wouldn’t open until far later in the evening—possibly not until after they went to bed.

He sighed and set down his fork.

“Pap … I know it's rough, believe me, I wish he'd come home from the lab, too, but ...”

But what? What excuse was he supposed to give? His dad was too busy? Yeah, that was probably true. What they were doing was important? It was, he _knew_ it was, he had said that, hadn’t he? It was still just as important, wasn’t it? He had wanted this. He had _asked_ for this. It was uncomfortable, sure, it was _agony,_ but it was still important.

He didn’t even know what his dad was doing anymore. But it had to be important, right?

“He said that nothing was more important,” Papyrus said, making Sans jolt in his seat. His eyes remained locked on the table. “That no experiment was more important than spending time with us.”

Not for the first time, Sans found himself wondering whether Papyrus actually could read minds, and he had just never seen fit to mention it because it would embarrass those whose minds he read.

But as soon as he looked at Papyrus’s face, _really_ looked, the thought disappeared. No. Papyrus had never been very good at keeping secrets.

A second later, Papyrus looked up, staring into Sans’s eyes with a piercing, yet gentle intensity that made him freeze.

“And he’s not spending time with you, either.”

Sans stiffened further. “Huh?”

“Even though you’re in the same lab,” Papyrus went on. “He doesn’t actually spend time with you, does he?”

Sans floundered for a few seconds, struggling to comprehend what his brother had said, before, at last, he looked away.

“What makes you think that?”

It wasn’t very convincing, and he knew it. And he wasn’t sure whether this would be one of those moments when Papyrus could read him like a picture book or one when he overlooked things that were staring him right in the face.

When he glanced back, Papyrus was looking down again.

“Do you remember when we were thirteen, and he was finishing up the Core, and he was gone all the time and he kept leaving us alone?”

Sans wasn’t sure whether Papyrus expected a response to that, but he nodded anyway, the movement vague and automatic. Papyrus looked up at him out of the tops of his sockets.

“You had a look on your face then,” he went on. “You tried to hide it. But you looked … empty. Like there was something only Dad could give you that filled you up and made you … _Sans._ And when he was gone, it wasn’t there.”

Sans didn’t even try to say anything, and a second later, Papyrus lifted his head in full, staring at Sans with eyes that could have easily pierced his soul.

“It’s not there now.”

Silence. Normally silence wouldn’t bother Sans, but silence from Papyrus was like unpleasant white noise, slightly uncomfortable at first, then almost painful, so much that he considered screaming right then, for no reason all, just so he wouldn’t have to endure it any longer.

He looked down at his plate, but the silence didn’t get any easier to bear.

Both of them had more than half their dinner remaining, but neither of them ate. They sat there, Sans as tense as he could be with the little energy he had left. He would have gladly had his soul sliced up into a dozen pieces right now if it meant Papyrus would just smile at him, if Papyrus would just go on with his day without worrying about him or his dad or _anything._ This didn’t involve him, and he shouldn’t have to suffer for it.

He shouldn’t have to suffer for anything.

“I’m not stupid, you know.”

Sans’s head snapped up so fast his neck hurt, and winced at the sudden rush in his skull before he met Papyrus’s eyes, his own as wide as they had ever been.

“I … I know you’re not stupid, Pap, you were never stupid, you’re amazing, did someone tell you—”

“You hide things from me,” Papyrus cut him off. He wasn’t looking at him. He stared down at the table, his hands clasped together, fiddling with his fingers. “Because you think I can’t handle them.”

Sans’s whole body sunk a little more into his chair. “Bro …”

Papyrus looked up again. There were the faintest hints of tears in his sockets now, forced back, but still glistening in the black.

“I know something’s wrong, Sans. And … you don’t have to tell me what it is, but …” He trailed off. His hands clenched into fists, and his mouth pressed into a thin line. “Please don’t get hurt, Sans. I can’t stand seeing you hurt.”

Sans floundered, searching for words that didn’t sound right in his head, and sounded even worse when they got to his mouth. He shook his head, slow and unsure.

“I’m okay.”

“You’re not okay,” Papyrus shot back, so sudden, so sharp that it made Sans jump. His mouth tightened further, his sockets wide and gleaming with something that might have been anger if it hadn’t looked so _Papyrus._ “ Stop saying you’re okay when you’re not.”

Sans didn’t move. Papyrus stared at him for a moment longer, mouth wobbling, before he finally lowered his head and let out a trembling breath through his teeth.

“You’re not okay and Dad’s not okay and neither of you will tell me what’s wrong.”

His voice cracked, and Sans watched one tear begin to slide out of his brother’s eye before he wiped it away and shook his head. Sans wanted more than anything to run around the table and pull Papyrus into the tightest hug he could muster. Yet he couldn’t bring himself to move a single toe.

No more tears came, and after a minute, Papyrus sniffed and brought his head up again, though he wouldn’t quite meet Sans’s eyes.

“You hated it when the other college students treated you like you were different,” he went on, and even though his voice had dropped since then, he sounded just like he had on those bad days when Sans came home and locked himself in his room in frustration. “Like you didn’t know as much because you were younger than them.”

“We’re the same age, Pap,” Sans muttered, his eyes as wide as before.

“Yes. We are,” Papyrus replied. He looked up, and suddenly the sweet, sad little baby bones was gone, and Papyrus could easily have been as old as their dad. “But you don’t act like we are.”

Sans started to talk, then stopped himself and let his gaze drift back to the table. His hands had clasped in his lap at some point, and now they squeezed so tight his arms had begun to shake. Papyrus shifted.

“When you were stressed about exams, you never told me. When the other students said rude things to you, you didn’t tell me.”

Sans swallowed and fidgeted. He was already sitting far more on the left side of his seat, and if he moved anymore he was going to fall off.

“I didn’t want to bother you.”

Papyrus made a sound that almost resembled a laugh.

“You’re my brother,” he said. “Even if you were a bother, all you’d need to do is add an R.”

It took a second—when had Papyrus ever made jokes?—but then Sans snorted, even though his chest still hurt and his head still spun and he had no idea what the hell he was supposed to say.

Neither of them said anything for more than a minute after that. Then Papyrus reached across the table, leaning so far his clothes almost ended up in the food, to rest a hand on Sans’s shoulder and give it a quick, firm squeeze. Sans relaxed, just a bit, on a reflex that had been there for as long as he could remember. Papyrus flashed him a quick, sad smile, and sat back down.

“It hurts when I see you hurting,” he went on, real and raw and so incredibly _Papyrus._ “ You take care of me. Let me take care of you.”

His smile tilted up more, still concerned, but perhaps a bit more hopeful. The remnants of tears still glistened on the edges of his sockets.

“And take care of yourself, too.”

Sans forced his hands to unclench, smoothing out in his lap even as his fingers twitched to curl up again.

“I’ll try.”

Papyrus smiled, a little more widely, a little more genuinely.

“That’s good. Trying is the first step,” he replied. “Now, you need to rest. Come on, finish eating, then I’ll get the dishes. You go upstairs and get in your pajamas and I’ll come up and read you a story.”

Sans chuckled, and even to his own mind, it almost sounded real.

“Sure, bro.”

They ate the rest of their dinner without a word, but every time Sans looked across the table, his brother smiled at him, and each time Sans smiled back, he felt it get a little easier.

Papyrus was still here. Papyrus supported him. Papyrus was worried about him. And Papyrus had always been very good at knowing when something was wrong.

And when something needed to be done.

No matter how long it took Sans to realize the same thing.

Their dad didn’t get home until almost eleven that night, but Sans hardly noticed. By the time the front door opened and shut, he was already tucked into bed, staring at the ceiling, while Papyrus sat in a chair next to him, book in his hands and head tilted forward in sleep.


	13. Chapter 11

**Notes for the Chapter:**

> As always, thank you for all your kind words. Hope you enjoy this chapter. ;)

Sans had been late today.

Gaster was getting used to that, to some extent. But it still confused him. Sans was _never_ late, not to anything important. Gaster wouldn’t really describe him as an early riser or a night person. He could be either, or both, depending on the situation. When he had morning classes, he was a morning person. If he had an important paper to write or a test to study for, he could stay up until five in the morning without so much as yawning.

And not once had he ever been late to a class, or to his internship, or to his job at the lab.

But today, he was half an hour later, and when he finally stumbled through the door, he didn’t even seem to notice. Before Gaster could get out a word, he laid down on the table and waited for the experiment to begin.

Something twisted in Gaster’s chest, just for a second. Then he pushed it away.

If Sans was having problems, they could discuss it later. For now, he needed to get this experiment finished.

That was what Sans had said, over and over. Finish the experiment. That was the first priority.

This time, Sans didn’t say anything the entire time he was setting things up. Granted, Gaster was far more efficient than he used to be, and Sans no longer needed to pester him to keep going or not to forget a step. It was strange, to think that he had been so out of practice just a short time ago. Now, it felt like his mind was trying to make up for the decades of silly, pointless experiments and random observational studies by rushing out as much work as he could handle. And Gaster couldn’t be happier with it.

He had missed this. God, he had missed this.

It had taken him a while to decide where to go now that he had completed several soul-cutting experiments. He wasn’t going to risk doing any more until some time had passed, and besides, for the moment, he had learned all he could from them. But finally, last night, it had come to him.

He knew exactly what substance had made Sans different in the first place.

And he couldn’t believe it had taken him this long to remember that he had a large jar of it left in the closet.

He had never had any use for it after the boys were removed from the tubes. But if this was what had made Sans’s soul unique when he was grown in it … perhaps it could make him even more unique now.

He expected Sans to ask what he was doing when he pulled out a vial and a syringe, but Sans didn’t do more than glance his way. He waited another minute, but still, nothing. Gaster frowned.

“I’m going to be injecting sixty grams of nutrient fluid into your bones,” he said. Sans looked toward him again, briefly, but said nothing, and didn’t move. Gaster’s browbone furrowed. Perhaps he was still groggy? “I think it may lengthen the amount of time your soul fragments survive after detachment, and may provide us with a better understand of exactly what changes the S.E. is responsible for.”

Nothing. Sans didn’t respond at all.

Gaster sighed, but finally stepped forward and filled the syringe with some of the nutrient fluid.

It would be over quickly. It was just sixty grams, with a very low concentration of S.E., and whatever the effects were, he doubted they would be significant.

But if the results were positive …

This would be over soon. This would all be over soon, and it would be worth it. It would be worth than worth it. For everyone.

Sans tensed when the needle went on, but only for a second, and ten seconds later, the needle was out, and Gaster set everything off to the side, turning his attention back to Sans, checking his HP and glancing at the monitor. Stable. Slightly more agitated than usual, but nothing of note.

Thirty seconds.

Sixty seconds.

Gaster was millimeters away from writing the first note on his clipboard when the machine beeped.

He jerked his head back, his soul pulsing so hard he swore it might shatter. The machine beeped again a few seconds later, and with each beep, Sans grew tenser, his eyes squeezed shut, his teeth gritted, his hands curled into fists so tight it must have hurt him. And for a second, Gaster panicked, no, it was just a little, just a bit, it was the same stuff he was grown in, it wasn’t supposed to have that much of an effect, it—

Then the beeping stopped.

And bit by bit, Sans’s body relaxed.

A small crease remained on his forehead, but his hands smoothed out, and his smile softened into an almost neutral expression. Gaster let out a breath he didn’t realize he had been holding, loosening his grip on the pen he had almost snapped. Then he looked down at the machine and the readings still flashing on the screen.

His grip tightened again.

Sans’s vitals had changed.

They were resting, they had stabilized, and they had _changed._

He glanced down at his notes, skimming through them until he found Sans’s baseline numbers, which he had almost memorized after so many tests. He had to be sure. This was … it had only been a small injection, and it had been diluted, it was only a fraction of pure S.E., and it had changed him, fundamentally _changed_ him, it—

Gaster very nearly dropped his pen, but finally grasped it, moved back to his desk, pulled his clipboard in front of him, and began to write.

He got down all his observations in the first few minutes, but he didn’t stop writing. This was … it was revolutionary. It was just a small change, but it was _proof,_ all the proof he needed that the differences in Sans were indeed caused by the nutrient fluid. By the S.E. _within_ that nutrient fluid. Sans had shifted, just a little bit, closer to a human. Just with one injection. It wasn’t a very big shift, he wouldn’t have even noticed it if he hadn’t been paying such close attention to Sans’s vitals, it would take ten times as much to make a truly significant difference, but it had _worked._

If he could replicate this, if he could go further, it would be all he would need to figure out the definitive formula for an artificial soul, a soul that could be used to replace a human’s. He would have to figure out where to get more supplies, but once he did …

He barely noticed Sans standing from the table. In the back of his mind, he thought that maybe Sans would go home, or perhaps just collapse on the couch as he did so often after experiments. But he heard neither the door or the springs on the couch. Instead he heard footsteps, stumbling, irregular footsteps, walking toward him until they stood just a few feet behind his chair.

“Dad.”

Gaster’s browbone furrowed, but he kept writing, a little faster this time, forcing his mind back on track. “Hm?”

Silence for a few seconds. Gaster returned his focus to his notes, he already had several ideas for future experiments, intervals of increasing the dosage, need to make it significant without risking major damage—

“ _Dad._ ”

“What is it, Sans?” Gaster bit out, glancing over his shoulder for less than half a second before returning to the papers. “I need to get these notes down.”

Sans didn’t say anything at first, and Gaster resisted the urge to tell him that if he was going to interrupt, he should at least make sure he knew what he was interrupting _for_. He made out the vague sound of feet shuffling against the tile floor.

“I … it still …” Sans began, voice quieter than Gaster was used to. Another pause, shorter this time. “Was it supposed to hurt that much?”

“Some discomfort was expected, yes,” Gaster replied on reflex. He huffed as he wrote down an extra zero without realizing, and scratched out the whole number before writing the correct one beside it and moving on to the next line.

“It still hurts.”

He paused, gritting his teeth to keep himself from saying exactly what was on his mind. “It should go away soon.”

More shuffling. Sans let out a soft breath that didn’t quite count as a sigh.

“I’m still hurting from the last one.”

Gaster snapped his head around, browbone raised, his hand tightening around his pen.

“Why didn’t you tell me?” he asked, unable to keep a touch of irritation out of his voice. “That needs to be in the records. If you’re experiencing long-term effects, that may suggest your healing capabilities aren’t quite as potent as I expected. Then again, with the number of experiments done in a short period of time … hm …”

He turned back to his clipboard and skimmed down for an empty spot. There was too much to write down, too many observations, too many ideas, he really needed to get an audio recorder so he could just dictate his notes while his hands were busy. That way he wouldn’t have to worry about getting it all down as soon as the experiment was complete.

“Dad.”

Gaster’s face pinched, and he wrote faster, his handwriting almost illegible at this point.

“Dad, _look at me._ ”

“What?” Gaster snapped, spinning around to face him again. He sighed and set his pen down so he wouldn’t risk snapping it in half. With as much time as they were wasting, he didn’t want to waste even more trying to find another pen. “Sans, it’s important that we get this down right away. It’s not just the numbers, it’s all the observations I had during the procedure. Speaking of, you should go ahead and write down your own experience before your memory gets fuzzy. Do you have your notebook? No, nevermind, here, I’ve got a spare—”

“I don’t want to do this anymore.”

Gaster stopped. He just stopped, and for a few seconds, neither of them said a word. Then Gaster looked at Sans, really looked at him, and bit by bit, his words registered.

“I’m sorry?” he asked, barely above a whisper.

Sans closed his eyes, took a deep breath, then opened them again.

“I don’t want to do these experiments anymore,” he said, so clearly that Gaster couldn’t mistake a single syllable. “I want to stop.”

Gaster’s browbone creased. He turned his whole body away from the desk, his shoulders slightly slumped. He sighed.

“Sans, if you’re in that much pain, I can go ahead and heal you and we’ll start the experiment over another day when you’ve had the chance to rest—”

“No. I don’t want to do this _at all,_ _”_ Sans cut in. Gaster paused with his mouth still open. Sans put a hand to his forehead and shook his head, the gesture such a perfect mimic of Gaster’s it was almost frightening. “It’s … this is worse than I thought, Dad. And it’s not getting any better. It’s getting a whole lot _worse,_ actually.”

Gaster couldn’t speak. He could barely think. Sans paused, but when Gaster didn’t reply, he lowered his head to stare at the floor.

“And Papyrus is always worried and I don’t want to tell him _why,_ but I can’t stand to see him upset like that. He knows something’s wrong, Dad.”

Gaster’s mouth tightened into a thin line. “He’ll be fine, he—”

“And this is affecting my ability to get my own work done,” Sans finished.

The crease in Gaster’s browbone deepened.

“This _is_ your work, Sans.”

“I mean the _other_ parts of my work,” Sans replied, meeting his eyes once more, his brief moment of uncertainty gone. “Like the T.F. readings, I was researching those before we started this.”

“Those aren’t exactly priority,” Gaster muttered.

Sans’s gaze hardened.

“And _this is_? ” He threw out a hand toward the examination table, toward the monitors, toward the pile of notes on Gaster’s desk. “Look, you told me to tell you as soon as it got too uncomfortable. and now I’m telling you. It’s too uncomfortable. I don’t want to do it anymore.”

Gaster’s soul twisted.

“Sans, you’re being ridiculous.”

“ _You’re_ being ridiculous!” Sans shot back, his voice louder than Gaster had heard it in years. “What happened to taking care of my wellbeing?”

Gaster flinched, just for a second, before straightening once again. “I keep a careful eye on your vitals and your healing, I would never let anything happen to you during these experiments—”

“You’re not _listening to me_! ”

Gaster stared. That was all he could do now. Stare and try to comprehend what Sans was saying to him.

All they had worked for. All the research they had already done, all the data they had spent so much time collecting. And he just wanted to …

He frowned a little harder.

“You were so eager to do these experiments, Sans, you said over and over that it didn’t matter if you had to go through a bit of pain—”

“This is more than a _bit_ of pain—”

“We’re close to a breakthrough!” Gaster spat. Sans jerked back as his voice echoed off the walls, but Gaster didn’t stop, he _couldn’t_ stop, they were so close, _so close,_ and Sans wasn’t going to—“You wanted me to care about these experiments, to care about getting us out of here, and right as we come close to making something happen—”

“I didn’t think you’d care about the experiments more than you care about me!”

Silence.

Neither of them moved. Neither of them spoke.

Gaster’s breath caught in his throat as he watched his son, standing just a few yards in front of him, hands curled into fists and eyes burning with something Gaster had never seen before. Not in Sans. Not in his son.

When the air slipped past Gaster’s teeth, it was trembling. He shook his head.

“I … I don’t, I … Sans, I would _never_ care about these experiments more than you.”

“Oh yeah?” Sans asked, as sharp as the scalpel still resting on the table. “When was the last time you asked me how I was feeling?”

Gaster brought his arms closer to his torso. “After every experiment, I—”

“So you can take notes,” Sans cut him off. “You never even ask me if I need to be healed.”

“Because some of the experiments are meant to measure how you heal independently—”

“And the ones that don’t?”

Gaster’s mouth snapped shut. Sans’s browbone lowered, and in all his life, Gaster didn’t think he had ever seen someone look at him with quite so much … anger? Bitterness? What name could describe that _look_ in Sans’s eyes?

“You don’t ask me how I’m doing. You don’t try to heal me. You don’t eat dinner with us, you don’t talk to Pap, you don’t talk to me unless it’s something to do with the experiments.”

Something smoothed out in Sans’s face, his smile tighter than it had been in years.

“Am I your test subject or your son?”

Gaster stared. Sans stared back. The words hung in the air between them for several seconds, untouched, unheard.

Then they crashed down on Gaster like the ceiling caving in on top of him.

He couldn’t feel temperature, not more than a little and never enough to bother him. But he swore his bones had turned to ice. He couldn’t move, he couldn’t breathe, he couldn’t _think,_ all he could do was stare at the young skeleton standing in front of him. The same young skeleton who had been in the lab with him for weeks.

Who had lain on the table, helpless, as Gaster poked and prodded at him like a living machine.

“Sans …?” Gaster breathed, the name strange on his teeth, as if he hadn’t really _said_ it in days, even though it had left his mouth countless times. He shook his head again, slower this time, as his sockets grew as wide as each would allow. “I … oh my god, I …”

He choked.

His eyes drifted to the examination table, and he saw it, _really_ saw it, perhaps for the first time. He saw the monitors that measured Sans’s vitals—and measured the damage Gaster did. The faint residue of the bones he had summoned to strike him, _intentionally_ strike him, when had he ever even _thought_ of striking his child? The cables to deliver electric shocks. The orange and blue attack simulators. The jar of nutrient fluid and the syringe.

The scalpel. The scalpel his own hand had held. The scalpel that had sliced into Sans’s soul and chopped off a piece, like cutting vegetables for dinner.

His hands shook so hard he had to hold them against his chest to keep his bones from rattling.

“I’ve really been doing that … haven’t I?” he murmured, more to himself than to anyone else. He looked at Sans, and Sans just stared, his face unreadable, his sockets as wide as before. Gaster’s head spun. “My god … oh, Sans …”

He might as well have stabbed himself with the scalpel for how badly his soul stung.

He had done that. _He_ had done that. He had sliced off pieces of Sans’s soul for the sake of _research._

“I’m sorry,” he breathed, before the words even registered in his head, his eyes falling to the ground. He choked on his own breath. “I’m so, so sorry, I … I don’t know what … I’m so sorry, Sans.”

Sans was silent, but Gaster didn’t have to look at him to see him clear as day in front of him. This was his son. His _son._ And he had … for however brief a time, he had …

What in the world was he _doing_?

His legs wobbled, and he barely managed to stumble back toward his chair before he collapsed into it, his elbows on his knees and his face in his hands.

These were experiments. Just experiments. Experiments that might not even have led anywhere, anyway. Even if he got all the information he needed from Sans’s soul, he would still need to find the materials to synthesize new souls. And by what? Scraping off more of his bone and letting it grow in more nutrient fluid? Could he even create a soul without a monster to go with it? How could he think of creating a monster just to take their soul? Would he even be able to separate the soul from the body without the soul vanishing, as monster souls usually did? A part of Sans's soul had survived for a while, but that didn't mean a full soul separation would be successful.

This could all be for nothing. Just for a hunch. His son would suffer, probably be traumatized for years to come, just for the _chance_ of breaking a barrier that had held for millennia already.

And he had been ready to continue. Despite Sans’s protests. Despite his obvious pain. He had ignored every sign, just because he thought it _might_ work.

“Dad?”

Gaster looked up. Sans stood in front of him, staring. Despite Gaster sitting down, they were about matched in height.

He was so small. And he was an adult now, unlikely to grow anymore. He had been small as that tiny skeleton he found growing in a mason jar, and he was small now, as a full-grown monster working as his colleague. His intelligent, competent colleague. And his infinitely precious son.

Gaster pressed his mouth into a tight line and sat up straighter in his seat.

“No more experiments. We’re stopping. Right now,” he said, and any hesitation he might have felt minutes before had gone. He paused, taking in every inch of his son’s expression—the dark circles under his eyes, the pale, brittle look to his bones, the pain _he_ had caused, by his own stupidity. He let out a long breath and shook his head without looking away. “I … I don’t know how I can possibly express how sorry I am, Sans …”

“Dad, it’s okay,” Sans cut him off, a faint laugh in his voice, though there wasn’t much humor to it. He smiled, weakly, without much meaning, and struggled. “It’s not like I haven’t gotten … overenthusiastic in my work before. I had to get that trait for somewhere, right?”

“That’s no excuse for hurting someone,” Gaster replied. Sans said nothing, and Gaster pushed himself to his feet, his face firm and his brow set. “But it ends now.”

Sans didn’t say anything at first, and it took Gaster several seconds to realize that he was searching his face for a lie. For any hint that he would go back on his word. He just stood there, looking at him, and finally, Sans’s shoulders fell, and his face relaxed into a shaky, but genuine, smile.

“Good,” he breathed, unable to keep the hitch out of his tone. He looked away. “Thanks.”

Gaster shook his head. “No. You owe me no thanks whatsoever.”

This time, Sans didn’t say anything, but Gaster didn’t have to see his whole face to recognize the relief gleaming in the lights of his eyes.

Relief that never should have had to be there in the first place.

Sans went back to the T.F. machine, and Gaster spent the rest of the day gathering up his notes from the experiments, shoving them into a folder, and shoving that folder into the very back of the file cabinet. With any luck, he would never look at it again.

Before he closed the drawer, his eyes lingered, just for a second, on the still-dusty green folder he had tucked away after the first experiment.

Then he gritted his teeth and slammed the cabinet shut.


	14. -16

**Notes for the Chapter:**

> Just to be absolutely clear, sign language is a complex, beautiful language which can express abstract concepts just as well as spoken language. Gaster is technically fluent in it, but it’s never felt like his _natural_ language, no matter how long he’s been using it, so especially when he’s stressed, he often can’t get across concepts as clearly as he would using spoken/written language.
> 
> Thanks for your support, everyone. :)

It took five minutes after the alarm started going off for Gaster to realize that it was going off for a reason.

Five minutes, and a tiny, bony finger poking him just below his eye socket.

“Daddy.”

“Mm …?” Gaster managed, squinting his sockets open to make out the blur leaning only a few inches above his face.

Papyrus poked him again. “Time to wake up, Daddy.”

Gaster blinked, very slowly.

Then he shot up so fast Papyrus almost went flying off the edge of the bed, and Sans, snuggled into his other side, grumbled as his makeshift pillow fell away.

Right. Of course.

He had set up that experiment the night before. The time-sensitive experiment that had to be finished this morning.

He looked at the clock.

This morning at five A.M., apparently.

One more poke. Papyrus had climbed back onto his lap, unfazed, and was now staring at him with wide sockets, his head tilted to the side.

Gaster let out a long breath, then scooped him up with one arm, a half-asleep Sans with the other, and pushed himself out of bed.

It took longer to get them dressed nowadays than it had when they were babies. Papyrus was learning to get dressed by himself and was quite good at it, but it still took him three times as long as it took for Gaster to dress him, and this morning, he was in a rush. Wasn’t he? What was the experiment again? Why was it so time-sensitive that he couldn’t wait until normal working hours to finish it?

Maybe coffee would help him remember. He should probably get a pot started.

Or … no, that would take too long. He could get coffee at work.

Papyrus wriggled around while Gaster pulled on his shirt and pants, trying to do as much of it by himself as possible. Sans was still just asleep enough that he didn’t seem to mind being stripped and re-dressed, though Gaster doubted that would last much longer. He had just as much energy as his brother when he was fully alert, and it wouldn’t be long before they were both bouncing off the walls of the room—or the lab, as it would probably be.

Soon, he wouldn’t even be able to keep them in the carrier with him. Would it still be safe to keep them in the lab while he worked? He would have to think about that. It wasn’t like he had done more than basic babyproofing since they were born.

Once he had them dressed and in his arms, he ran down the stairs so fast that he had to skid to a stop to keep himself from smacking into the door. He took a second to adjust his lab coat with one barely-free hand, pick up his bag off the couch—was that where he had put it last night?—before he put his hand on the knob.

“Daddy.”

Yet again, Gaster stopped, adjusting the boys in his arms. “Yes, Papyrus?”

Papyrus poked him just under his eyesocket. “Hungry.”

Gaster stared. Then he blinked.

“Oh.”

He looked at the table. The empty table. The clean kitchen. The kitchen he hadn’t even thought of stopping by before he left for the lab.

“Oh, yes. Breakfast. Right, of course,” he went on at last, smiling down at Papyrus even as he could practically hear the clock ticking away in the back of his head. “What would you two like?”

Papyrus’s face lit up.

“Waffles!”

“Chocolate chip waffles!” Sans added. Yes, he was definitely just as awake as his brother now.

Gaster gritted his teeth. He glanced at the door, then at the clock. Well, the experiment wasn’t going to expire if he left it for another half-hour, even if he couldn’t quite remember what that experiment was in the first place … and the boys could always eat while he walked …

He went to the fridge and began to dig out the ingredients.

Papyrus had taken an interest in learning to cook over the past few weeks, despite his dexterity not allowing him to do more than the simplest of tasks. His favorite “job” was stirring, so all Gaster had to do was dump all the ingredients in a bowl and give Papyrus a spoon to ensure the batter would be ready by the time the waffle iron was heated up. When Sans reminded him about the chocolate chips, Gaster dug around in their cupboard—he really needed to clean that soon, he didn’t know how in the world Papyrus’s old rattle ended up on the top shelf, and he was fairly sure that jar of peanut butter had been there since before the boys were born—and handed him the bag, before bustling around the kitchen to get lunch prepared, once he realized he had forgotten that as well.

When the waffle iron beeped, he turned back to Papyrus and Sans, his hands held out to retrieve the bowl.

Only to find that Sans had dumped the entire bag of chocolate chips in with the batter, and Papyrus was looking at him like he had just filled the bowl with raw spinach.

Well, perhaps not. Papyrus liked spinach.

Gaster paused. He looked at the clock again, then at the boys.

Then he grabbed the bowl and spoon, scooted the mixture around a little so most of the chocolate chips were on one side, and poured the cleaner part of the batter onto the top half of the iron. Sans started to complain, before Gaster flipped the bowl around and poured what amounted to pure chocolate onto the other two waffle molds.

Papyrus frowned. Sans beamed.

The first batch of waffles finished several minutes later, and while the boys ate, Gaster poured the rest of the batter—half-plain, half-chocolate—onto the iron and snatched a couple of granola bars from the cabinet for himself. When the waffle iron beeped again, he pulled the waffles out, stuck them in a little baggie, grabbed his work bag, and ran out the door.

Then he stopped, ran back into the house, put the two wide-eyed boys sitting on the counter into their carrier, and ran out the door again.

Sans munched on his pure chocolate the whole way there, while Papyrus kept leaning forward from his spot on Gaster’s back to encourage Gaster to take bites of one of his waffles. He hadn’t liked the idea of granola bars every day for breakfast since he was two, and it seemed he was forever on a mission to get Gaster to eat something that took more than a minute to make.

It took him three tries to swipe his key card through the reader, and he almost ended up punching the door before it finally let him through. He still couldn’t remember what that experiment had been. It was something important, he wouldn’t have set his alarm for quite that early otherwise, especially given how late he had stayed up last night …

… why had he been up so late again?

He brushed the thought aside as he ran through the ground floor of the lab, pausing only long enough for Papyrus to push the button to the elevator as he requested.

He was running out of the elevator almost before the doors opened, and started running the wrong way before correcting himself and turning to the right, toward his own lab. Sans pointed the way whenever he forgot which corridor to take, and Gaster murmured a thank-you no less than four times in under a minute.

“Good morning, Dr. Gaster!”

Gaster slowed, and barely had the presence of mind to recognize the voice before he turned to face it. Even when he saw Dr. Billington’s wrinkled yellow hand waving, a cheery smile on her face where she stood down the hall, it took him a moment to place it.

He blinked, then smiled back, even as he continued to move toward the lab.

GOOD MORNING, DR. BILLINGTON, he signed, a little more awkwardly than usual.

She just chuckled and waved again, her eyes on the boys. “Good morning, Papyrus! Good morning, Sans!”

“Hi, Bill!” Sans called back.

“Hi!” Papyrus added, waving so hard his hand whacked the back of Gaster’s skull.

Dr. Billington just laughed, and Gaster flashed her a quick, anxious smile before continuing on his way.

He was really starting to worry about whatever he had left in the lab.

Surely he would have remembered it by now if it was important? He wouldn’t have forgotten something essential. But he also wouldn’t have set his alarm if it wasn’t truly time-sensitive. Whatever it was—

He threw open the door to his lab and flicked on the lights.

And his eyes fell on the work desk in the middle of the room, and the beaker filled with black liquid sitting near the edge.

Right. That was what he had started yesterday, just before he left.

The coolant stabilization experiment.

The coolant stabilization experiment that was meant to sit for exactly thirteen hours.

The coolant stabilization experiment that had been sitting there for thirteen and a half hours, and which was now bubbling out of the top of the beaker.

Damn it.

He ran across the lab so fast the boys clung to his clothes. They said something, a question, probably, but he barely heard it, and didn’t respond. He was far too focused on grabbing glass petri dishes to contain the overflowing fluid before it burned a hole in the counter.

Corrosive liquid.

He should put the boys in the playpen. They shouldn’t be near this.

They—

Some of the liquid nearly spilled onto Gaster’s hands, and before he could think, he was pulling on some gloves and working to keep the liquid contained.

No time.

He had already told them yesterday that the bubbly black stuff would hurt them if they touched it, and as usual, they seemed to heed his warning. So Gaster focused his attention on the fluid and got to work.

It took more than ten minutes to get the fluid stabilized again. At first, he had thought it was ruined and he would have to start all over again, but after a bit of manipulation, it seemed that most of it was still salvageable. He separated it out into five smaller test tubes and got to work on his analysis before it could start bubbling over once again.

He didn’t watch the clock. He didn’t listen for anyone else coming in. He just focused on testing each liquid sample for the changes in its composition, in its stability, its temperature, its density. It was one of the most serious experiments he had attempted in a while, and though he had only been working on it for a week now, it felt like it had consumed his entire life. It was part of a larger project he had come up with several months ago, synthesizing an alternative fuel that would more efficiently use the resources they had left.

It wouldn’t solve the problem of decreasing energy resources. It wasn’t as clean as he had hoped, and it wouldn’t last very long.

But when there was almost nothing left, anything that would prolong a permanent loss of power was good news.

Gaster worked, murmuring to himself under his breath, jotting down notes, sorting the test tubes away as soon as he was done with them—and being sure to cap them to be sure he didn’t come back to find holes burned into the floor when he came back the next day. When the fifth test tube was put away, he let out a breath he didn’t realize he had been holding, and the ache in his legs that must have been building up for hours hit him all at once, heavy and burning and immensely sore.

But he was done.

Done. One step closer to a fuel source that would keep them going just a little longer.

Even if he would still have to figure out a container—aside from glass—that would hold it without melting.

He would have to run his results by Dr. Billington. Even though she hadn’t been working in this lab as long as he had, she had still been here a long, long time, and she had always had a knack for chemical engineering. Or maybe that new intern of hers. Frewth, wasn’t that his name? He was going into technology. Maybe he had some ideas.

Especially with those rumors of Dr. Billington retiring soon …

“Everything alright in here?”

Gaster jerked around so fast he almost tripped over his own feet.

After hearing it as many times as he had, he shouldn’t have been surprised by the owner of the voice standing in the doorway to the lab. But he still couldn’t figure out how Dr. Japer managed to open the door as quietly as she did, and stand there smiling at him now as if she had been there for more than a minute.

“Oh,” he muttered, lifting his hands before he could start speaking on reflex. YES. EVERYTHING GOOD.

Dr. Japer didn’t look particularly convinced. She didn’t look half as concerned as she had in the past—when there almost always _was_ something wrong—but he still caught that glint of worry in her eyes. Sometimes he wondered if she still held the fact that he hadn’t told anyone about the boys until their birth against him. She had given him quite the look when she found out he had been growing children in his lab for four months and had said nothing about it, and to this day, he wasn’t sure whether she was more concerned about the children or him.

No matter how it had started, though, now, the looks she gave him were full of affection. For the boys just as much as him.

She stepped further into the lab, letting the door fall shut behind her.

“I heard you were here already today. Almost as early as Dr. Billington, and I’ve never met anyone who gets in as early as she does.”

Gaster offered a sheepish smile, glancing down at the test tubes in front of him before giving her a helpless shrug. SENSITIVE EXPERIMENT.

“Ah, I see,” she replied with a chuckle, her eyes lingering on the test tubes—he could almost hear her asking “What sort of mischief are you getting up to now?”—before they returned to him. “How are the boys faring with the change in schedule?”

Gaster looked down at Sans, resting against his chest. THEY—

He stopped, hands still in the air, staring at the tiny skeleton in the front of the carrier. Then he glanced over his shoulder to Papyrus still riding in the back.

They had fallen asleep, apparently.

When had that happened? How long had he been here?

Dr. Japer didn’t get here until around nine. He had woken up at five, so …

Had he really lost track of time that much?

Had he been so focused on his experiment that he hadn’t noticed his own sons for _three hours_?

He put a hand to his face, closing his eyes and letting out a long, shaky breath.

“What am I doing …?”

“Dr. Gaster?” Dr. Japer asked, taking a step forward.

He dropped his hand and looked at her, and his face must have looked downright desperate if it made her own look quite so concerned. He huffed again through his teeth, lifting his hands and trying to sort out the words before he began to sign them.

THEM IMPORTANT. MOST IMPORTANT.

“Yes,” Dr. Japer agreed, her brow furrowed. “You’ve said that before.”

WHY FORGET-I? he asked.

She stared, then slowly shook her head. “I don’t understand.”

Gaster grimaced, but tried to smooth his face out several seconds later. He squeezed his hands into fists, then forced them to relax again before holding them up to attempt another sign.

SANS. PAPYRUS. MOST IMPORTANT THINGS.

Dr. Japer nodded, though there was still a touch of confusion knitting her brow. “Yes.”

FORGET-I, Gaster went on, holding out in his hands in a gesture he knew probably looked imploring.

He could _see_ her trying to put the pieces together, trying to sort out what in the world he meant. She tilted her head.

“You forget how important they are to you?”

NO, he went on, shaking his head and almost speaking on reflex. It was getting very, very difficult to keep his expression calm. NO. FORGET … WHEN WORK-DO.

Her forehead wrinkled further. “You forget … when you’re working?”

Gaster huffed before he could stop himself. He held his hands up in front of him, making vague gestures as if that might make signing any easier.

YES. NO. FORGET-I …

She took a step closer, her face smoothing out to something he managed to recognize as concern. “It’s alright. Take your time.”

Why was she comforting him? What was wrong? He was fine. He was just … he was trying to get his words out, he _knew_ what he wanted to say, but he couldn’t figure out what signs to use, he could hardly put it into words to speak and trying to sign it after that … He shook his head, so fast it almost made his skull hurt.

KNOW-I … WHAT WANT SAY … I …

He gripped his skull, ducking his head to stare at the floor. Why was this so difficult? Why couldn’t he get it across, why was she looking at him with that _pity_ in her eyes, why didn’t she get it, why did she look at him like he--

“Dr. Gaster, it’s alright,” she said, so gentle, so patient, she couldn’t be older than three hundred, and she could _talk_ , she could talk and people would listen and they would know what she wanted to say. “If you can’t sign it—”

“Why can’t any of you understand me?!”

Dr. Japer jerked back, her fur standing on end, her arms close to her chest. Gaster felt his breath pushing in and out of his chest as he stared at her, his own words echoing back to him even though he knew they were gibberish to her ears.

“Daddy?”

He blinked. He looked down, only to find Sans staring up at him with sleepy sockets, his browbone furrowed in concern. A second later, a tiny, bony hand poked his cheek, and he turned his head enough to see Papyrus leaning against his shoulder from the back of the carrier.

“Daddy, w’as wrong?” he asked.

Gaster let out a breath he didn’t realize he had been holding. He lifted a hand to rest it on Sans’s skull, gentle, careful, and he reached over his shoulder to brush his finger’s over Papyrus’s head as well. He sighed.

“Nothing … nothing, Daddy’s … Daddy’s fine.”

It came out shaky at best, and he could tell, even at a glance, that neither of the three-year-olds believed him. They watched him with those wise, far-too-knowing sockets, waiting for an explanation, an answer. But Gaster’s attention shifted again to Dr. Japer, whose shoulders had relaxed, her fur smoothing out, though she still stared at him in something between distress and concern.

He pressed his mouth into a thin line, ducked his head, and lifted his hands.

SORRY. SHOUT WRONG.

Her posture softened a bit further, and her mouth tilted into a sad smile. She quirked her head.

“Would writing it be easier?” she asked. Gaster glanced away, but apparently, that was all the answer she needed—either that, or she hadn’t been looking for one in the first place. A second later, out of the corner of his eye, he saw her smile widen, and her attention lower to the two little skeletons strapped to his back and chest. “Sans? Papyrus?”

Sans turned around as much as the carrier would allow to look at her. “Yeah?”

Dr. Japer dug through her bag, pulling out what looked to be a small, brightly colored laptop, with much larger keys than a typical keyboard and what Gaster guessed was far less functionality. But as soon as she held it up, both Sans and Papyrus stared at it with wide, bright sockets, smiles slowly growing on both their faces.

“I’ve got a new toy for you,” she said, even though it was obvious. “Do you want to go in your playpen and try it out?”

Gaster couldn’t see him fully from this angle, but he didn’t need to look to feel Papyrus reaching out with grabby hands toward the toy, almost falling out of the carrier for how far he leaned over. “Yeah! Yeah!”

With only a brief glance at Dr. Japer, Gaster lifted both the boys out of the carrier and walked them over to the little “playpen” they had set up near the corner of the lab, away from the most dangerous machines. It wasn’t so much a playpen as it was an area with blankets and toys and a small fence—which Sans had figured out how to open when he was one—where the boys could stay if Gaster was doing something more dangerous, or if they didn’t want to be in the carrier, though that almost never happened. Once they were inside, Dr. Japer handed them the toy laptop and showed them how to turn in on, and in seconds, they were typing on the keys and giggling at the images popping up on the small screen.

Dr. Japer slipped back toward the main part of the lab, and Gaster followed her, looking over his shoulder every few seconds to confirm the boys were still content.

“That should keep them busy for at least ten minutes. It kept my niece busy for two hours when she first got it,” Dr. Japer said, such fondness in her voice that sometimes Gaster wondered why he hadn’t suggested the boys called her Aunt Japes. She nodded toward the computer, and suddenly Gaster remembered why she had distracted the boys in the first place. “Go ahead.”

Gaster sat down in the chair in front of his computer and opened his word processor. Then he paused, staring at the screen, glancing to his side to see Dr. Japer standing there, watching the screen, watching him, waiting with never-ending patience. He curled his fingers tight into his palms, then stretched them out and began to type.

_I love them._

He didn’t look at her in full, but all he needed was the glimpse he got out of the corner of his eye to read her baffled expression.

“I know,” she said, as if it were the most obvious thing in the world.

Gaster sighed, paused, wrung his hands, then returned them to the keyboard.

_Then why do I keep getting distracted and forgetting about taking care of them?_

He risked a better look at her to find her brow furrowed and her head quirked to the side. He turned to stare across the room, to where the boys were still enraptured by the toy computer. It felt wrong, seeing them in the playpen without him. The older they got, the more time they spent there, but usually, unless he was doing something dangerous, they preferred to stay in the carrier, watching him work or napping.

His chest ached.

_I didn’t even notice when four hours went by. They must have been so bored, but they didn’t say anything. Or maybe they did and I just didn’t hear them._

“You would have heard them,” she said, without hesitation.

Gaster pressed his mouth into a tight line.

 _How are you so sure?_ he typed, his fingers hitting the keys so fast he thought he might break them. _I almost forgot to make breakfast for them before we left._

Dr. Japer laughed, smiling down at him in amused fondness. “Do you know how many times my brother’s done the same thing?”

But Gaster didn’t smile back. He stared at his hands, resting in his lap. If he listened closely, he could hear the boys chattering, and could even make out some of their words. How had this much time already gone by? How had they started talking, forming complete sentences, in such a short span? He huffed and lifted his hands again.

_Sometimes I’m working on one of my projects but I can’t concentrate because the boys are nearby. And I_

He paused, gritting his teeth, but as much as it pained him, he forced himself to finish.

_Sometimes I wish I could go back to how things were before. When it was just me._

It felt like admitting he wanted to run through the barrier and abandon the rest of the monsters here for eternity. It felt like … like he had struck one of his children, even though they were sitting across the room and they couldn’t hear what he was typing and he would _never_ lay a hand on them, but it felt like …

“Do you think that now?”

Gaster tried to read Dr. Japer’s tone, but as seemed to happen more and more often lately, he came up with nothing. He looked at her, slightly desperate, but she said nothing. She just looked at him, waiting, her face revealing no more than her voice. Gaster sighed and looked away again.

_No. It never lasts. I love them so much and I wouldn’t give them up for anything but I wasn’t prepared for this. I got myself into it, I made my choice, why is it so difficult to adjust?_

Silence. Gaster stared at the screen and waited. He could make out the faintest hint of her reflection on the computer screen, but nothing else. If he listened closely, he could hear the boys giggling, babbling about something new on their own little computer, their voices so warm and happy and god, he didn’t deserve even a minute of the three years he had spent with them already.

They deserved so much better.

He had just been too selfish to give them up.

“How long has it been since the war?”

Gaster stiffened. At first, he wasn’t sure he had heard her right. He turned to face her, searching her face, but all he found was a blank expression, her brow barely raised. His own browbone furrowed.

 _What?_ he typed, almost putting it in all caps to make sure she saw it.

“How long?” she asked again, with an expectant look that felt far too familiar. “You know I wasn’t alive then.”

Gaster’s shoulders sunk. He knew where she was going with this. He wasn’t an idiot, and he felt like he was being walked by the hand down a difficult path because he couldn’t handle it himself. He looked away, but still, he found his fingers returning to the keyboard.

_Two thousand, one hundred and twenty-two years._

She looked at him with the same expectancy, though now there was a deep sadness behind it, the sort of sadness that came from knowing something awful had happened, knowing how awful it was, but never really being able to understand it.

“And how long, during those two thousand, one hundred and twenty-two years, have you spent by yourself, cooped up in your lab?” she asked, even though she didn’t need to. Even though he already knew exactly what she was going to say. Her face softened further. “It’s been three years, Dr. Gaster.”

Gaster looked away, not even glancing at the keyboard as he typed. _Three years, four months, seventeen days._

She huffed a laugh, and he couldn’t help the small twitch of a smile that touched his mouth before he forced it away again. He could feel her watching him, even though he didn’t turn to face her.

“And would you care to tell me how much smaller that number is than two thousand, one hundred and twenty-two years?”

He had known it. He had known exactly what she was going to say. But hearing the words still made some of the tension slip from his bones. He smiled again, just for a second, before he clenched his teeth and shook his head.

_You’re so much better at this than I am._

This time, she snorted, crossing her arms over her chest. “Oh, I might not be so much ‘better’ if I had children of my own.”

 _I thought you weren’t going to?_ he typed, turning to face her with a furrowed browbone.

“I’m not,” she said, very quickly, a laugh slipping out as if the very idea amused her. “I’m quite happy the way I am now.”

She smiled at him, but he still watched her with a sort of benign envy, his fingers moving before he could even figure out the words.

_You’re still better, though._

He didn’t look at her for a few seconds after that, and when he finally did, he found her staring with a contemplative expression he couldn’t quite read. A small smile remained on her lips, but he couldn’t tell whether or not it looked happy. She shrugged.

“Even before my niece was born, I always had younger cousins, and I always spent time around children,” she replied. Her smile tilted into a smirk. “And I wouldn’t have half as much knowledge as I do now if your children had been born earlier. Do you know how helpless I was with my niece when she was first born?”

He said nothing. He looked at her, at the hints of gray around her fur, the lines of smiles and frowns and _life,_ he had never asked her age, but she had been young when she first came to work with him, two centuries before, now …

He swallowed hard and returned to his keyboard.

_Sometimes I forget that I’m supposed to be the older one._

Dr. Japer raised an eyebrow, then chuckled and shrugged. “Anything to keep an old geezer like you feeling young.”

He pulled a face that was meant to look offended, but it just made Dr. Japer laugh more, and he couldn’t bring himself to hold it against her. He held himself a bit taller in his chair and kept his eyes on her even as his fingers touched the keys.

_One day._

She tilted her head. “I’m sorry?”

 _One day, I’m going to get used to it,_ he continued, typing so fervently that he didn’t even have to think about the words before they reached his fingers. _One day I won’t spend all my time on these projects. I’ll spend my time with them. They’re what is most important._

Before she could respond, before he could even process the expression on her face, he pushed himself out of his chair and smiled at her, lifting his hands in the most intentional, clear signing he had managed in years.

NOW START.

“Mm?” she asked, staring, brow still furrowed.

He smiled and turned to where the boys still sat playing in the pen.

“Sans? Papyrus?”

Instantly, both of them faced him, their new toy forgotten and their attention completely on him.

“Uh-huh?” Sans asked.

He gave them a wider smile, gentle and fond, and tried to soak up every second of how they were right now, remembering, for the first time in a while, that this wasn’t going to last.

“I’ll be finished with this experiment in about thirty minutes,” he said. They nodded. Sans already had a fairly good concept of time, and though Papyrus wasn’t particularly patient, he at least had a decent idea of what a minute was. “How would you like to go visit Snowdin after that?”

Their whole faces lit up, and they looked to each other, smiles growing, before turning back to him.

“Go t’Snowdin?” Sans repeated.

“We can see Mr. Grillby!” Papyrus piped in, all but beaming at the idea.

Gaster chuckled, and his face had never felt so soft.

“Yes, and I’m sure Mr. Grillby will be very happy to see you, too.”

The boys giggled and squealed, immediately turning to babble about all the fun things they could do with Grillby, how they could show him their new toy, and everything they remembered about Snowdin—even though it had been two months since they had last managed a visit. Gaster watched them for a moment, his soul tight and warm, before he looked to Dr. Japer once again.

He lifted his hands, ready to sign and explain what he had said, but as usual, Dr. Japer seemed to have picked up enough on her own. Maybe she couldn’t understand a single word that came out of his mouth. Maybe she never would. But she would still find a way to make sure he was understood.

It wasn’t the same. But it was the best he was going to get.

He slid back into his chair and began to type again.

_Thank you._

Her face softened into something far too motherly for someone with no children. Someone who was centuries and centuries younger than him, someone who had once been such an energetic young scientist, someone who had gotten old far too fast.

“Anytime,” she said. “You know that.”

His smile widened, and he nodded, turning again to the keyboard.

_No more work today. Today is about them._

“Maybe it’ll do you some good, too,” she added with a chuckle. Her smile tilted into more of a smirk, though he caught a genuine gleam of concern in her eyes as she spoke. “Just promise you won’t try to make up for lost time once the boys are asleep tonight.”

He tensed and hoped she wouldn’t catch it. He managed a wider smile and typed out the first words that slipped into his head.

_Come now, Dr. Japer, I don’t tell fibulas._

It took a second, and she had to lean in to be sure of what she read, but a second later she put a paw to her face and stepped back, groaning so loud the boys could probably hear her.

“Oh, why did I ever suggest you type …?”

Gaster laughed, a bubbling, real sound he almost didn’t recognize from his own mouth. And despite her exasperation, Dr. Japer smiled again, peering across the room to where the boys had turned to watch them, heads quirked in curious interest.

He followed her gaze and smiled at them, lifting his hand in a wave. Sans and Papyrus beamed and waved right back.

One day.

One day, he would be the father they deserved.


	15. Chapter 12

**Notes for the Chapter:**

> Sorry for the delayed update, everyone! Hope you like the new chapter! :)

It was like nothing had ever happened.

Not really, of course. Nothing could erase the memories that had attached themselves very firmly to every part of this lab. Gaster had been working here for decades, and he had no doubt it would take decades more for him to stop thinking about what had happened on that table every time he looked at it. Sans had worked here for less than two months, and Gaster really didn’t want to think about how much it would affect his perception of this place for the rest of his career.

But on the surface, from what anyone else could have seen, from the moment they walked into the lab the following Monday, it was as if the past few weeks had never occurred. They had jumped back in time to the end of Sans’s first week on the job, before any of this mess had started—and for a second, when Gaster first arrived, he actually believed it, when he found Sans already in front of the T.F. machine, jotting down notes and making adjustments to the controls.

Then Sans looked up.

And for a half-second, his smile froze, before it softened once again.

No. It would be a very long time before things truly went back to normal.

But he was occupied, at least, and it was more than a slight relief to see his energy returning almost to the level it had been before. This was Sans’s natural state. Eager, energetic, passionate about every little thing he did. Unhealthily so, at times, but forgetting to take a lunch break was far less of a problem than barely being able to get off the couch.

Considering who had been the one to suffer most during all of this, Gaster should have managed just as well.

Yet even as Sans jumped right back into the work he had left behind, Gaster found himself lost, standing near the entrance to the lab and looking around for a good ten minutes before he even brought himself to set down his bag.

Sans didn’t notice his idleness—or, if he did, he said nothing about it. Maybe he was more comfortable not acknowledging how lost Gaster looked, and why. Gaster couldn’t blame him. If he could have separated Sans from all of this, from _him,_ so he could heal without having to worry about Gaster’s issues, he would have done it in a second.

That was one of the downsides of being co-workers as well as family, he supposed.

Eventually, he took to tidying up to give the impression that he was doing something productive, or at least that he wasn’t standing around doing nothing. The lab _did_ need cleaning, after all, and maybe he would find some motivation if he was in a cleaner workspace. That worked well enough for a few days. He dusted and organized and sorted things into their proper places, even things that he hadn’t known _had_ proper places. Sans stayed out of the spots he was cleaning—not that Gaster needed to clean what Sans was working on, given that Sans hadn’t completely inherited his untidiness, and kept the T.F. Machine, and his own workspace, fairly neat on his own.

But even the messiest lab couldn’t keep him occupied for more than a few days.

And on the fourth day back, only a few hours after he arrived, he found the lab decently clean, and his mind just as blank as ever.

Gaster tried to find something to work on. He really, really tried. He even considered going back to the house and picking up the work he had done on the icy bracelets. He had put a good amount of effort into them, after all, and as easy as it was to laugh at them, they _could_ turn out to be useful if he could get the kinks worked out.

But every time he tried to turn toward the door, his thoughts strayed, and his feet refused to move.

He searched the newly-organized lab for remnants of old projects he had abandoned, ideas he could pick up, _anything_ that would distract him and give him something to do. But his mind refused to focus. Nothing he looked at struck a spark in his mind, the spark that had tugged him through the most grueling and tedious research over the years.

None of his ideas or projects seemed remotely important, after what he had given up.

Could they really have done it? Could they really have gotten out of here?

He hadn’t had hope in so long. He had tried, of course. He had tried so many times. Years ago, he had been entirely determined that they wouldn’t have to wait for all seven humans to fall before they got out of this place. He had used every idea he could conceive of, and none of them had worked.

_You’re a lot of things, Dad. But you’re not a quitter._

That was what he had done, wasn’t it? All those years ago, before his sons were even born? He had given up. He had quit.

And he was quitting again.

But … no. No. This was different. He had quit then because he didn’t know what else to do. He was quitting now because what he was doing was wrong.

It _had_ been wrong, hadn’t it? They had been getting results, certainly, but the results hadn’t been worth the cost. Sans hadn’t wanted to continue. He had been in pain, he had been suffering, and he had put off telling Gaster for far too long anyway. It would have been wrong to push him to keep going.

Even if it might have benefited him in the end, just like it would have benefited everyone else. Even if it might have meant an end to centuries spent underground, trapped in this makeshift prison. Even if it might have meant an end to what seemed like an endless wait. Even if it might have meant that his sons could finally see the sunlight, the open sky, the grass and the trees and everything he had never quite forgotten, despite how long it had been.

Even if it meant Sans could see the real stars, not just pictures or a mural painted on his ceiling. Even if it meant Papyrus could see all those human things that had fascinated him in storybooks as a child.

Even if it might not have taken _that_ much longer. Even if it only would have taken a few more experiments, a few more tests, then they could work together on constructing an artificial soul. It seemed impossible, but if they had come this far, certainly they could find a way to use that knowledge to construct a soul from what they had. If they had this knowledge, maybe they could modify a monster’s soul, a monster who was already close to death, so there would be no need to create a new monster just to remove their soul. If they knew exactly what made Sans’s soul different, if they knew what being grown in S.E. had already done and what they would still need to do to make a soul mimic a human’s, then they could do the rest with ease. If they could just do a few more tests …

Gaster’s eyes drifted across the room to where Sans was poking at the T.F. machine, marking something down on a piece of paper.

And his whole body stiffened.

What in the _world_ was he thinking?

This was his _son._ It didn’t matter what the reason was, scientific curiosity or the fate of all monsters. How could he even _think_ of making his son suffer, when he had so clearly stated that he _was_ suffering?

Of course, he had been so enthusiastic before. He had been so eager, so willing to go through with it. He said it didn’t matter if he had to put up with a little pain if it meant a chance of getting them all out of here. But …

No. _No._ Sans had made it very clear that what he was going through was more than he had expected, more than he was willing to endure. And Gaster still couldn’t believe it had taken him so long to notice the symptoms. So long to notice how tired he was, how his boundless energy had just … died, how his bright grin at the talk of a new experiment was replaced by a barely-restrained grimace. That should have been enough to alert him. Yet it hadn’t. He had been so consumed with the idea of them getting _out,_ that he hadn’t noticed one of the two most important people in his life in pain.

He shouldn’t have made that mistake even once. But he definitely wasn’t going to make it again.

He looked back to Sans, taking in every one of his movements, the minuscule changes in his expression. How long had it been since he had taken a moment to appreciate that? To appreciate that his son could finally work with him, after years of study and hard work, when he could have been contributing to the department years ago? That he had access to the machines that allowed him to study what he had poured over in books for months on end? That he could head up research on the work he really _cared_ about?

Even if it wasn’t the work that would break the barrier.

Sans was happy here. Happy enough, anyway—or at least he _would_ be happy once he healed from recent events. And Gaster should be grateful for that. He shouldn’t be spending his time mulling over something that may not have worked anyway.

But the longer he watched his son work, slipping around the T.F. Machine, jotting down notes, consulting one of the books on his desk—when had he brought in books? Had he always had that many notes sitting there?—Gaster couldn’t help but notice how cramped his workspace was.

The lab was a good deal cleaner than it had been a week before, but it was still cluttered, and still very crowded. And now that Gaster paid attention to it, Sans had to constantly step over cords and wires and glance over his shoulder to keep from bumping into machines.

If he hadn’t been working in such a cluttered lab, he might not have tripped over those cords a few weeks ago, and the machine might not have fallen on top of him.

Gaster wouldn’t have gotten the idea of trying to heal his eye.

And he would never have discovered the unique properties of Sans’s soul.

As much as he hated himself for it, he couldn’t decide whether or not that would have been a good thing.

Either way, Sans’s eye remained damaged, and though he seemed to have gotten used to the lab environment, it still posed a risk. And on top of that, all this clutter wasn’t conducive to the sort of work Sans did. Gaster had been scatterbrained for as long as he could remember—he thrived when he had all sorts of projects surrounding him, something he could pick up and work on before switching to something else. Sans certainly had his moments, but for the most part he tended to pick one thing and focus on it. And there wasn’t much room for focus in a lab with about fifty different things going on at once.

He hadn’t complained. But then again, he hadn’t complained about the experiments either. Not until they became unbearable.

Gaster spent the next few hours thinking, pacing around the room, feeling Sans’s eyes occasionally flick to him, but never for longer than a second. Unlike most of his ideas, which hit him like a brick to the face, this one came slowly, trickling in as his memories began to resurface. He wondered sometimes if everyone who got as old as he was felt their memories blur at times, yet come back full force whenever they became relevant. It was like his head had run out of active space and stored almost everything away, dormant, until the moment he needed to remember it again.

It was almost four in the afternoon when the idea finally solidified, and Gaster looked at his son for several minutes straight before clearing his throat.

“You know, Sans, if you’d like your own space to work, I know a spot you might like to use for a private lab.”

Sans’s head snapped up.

“Huh?” he managed. Then the words seemed to register. “What, really?”

Gaster just raised his browbone in question. Sans hesitated.

“Do you … not like having me in the lab with you?”

“No, no, of course not,” Gaster said without missing a beat, pulling back a little in surprise. “You’re welcome to stay. I was just thinking … it’s already rather cluttered in here, and you don’t have much room to do your own experiments. And from what I remember, the T.F. machine can be rather sensitive. A lot of movement in the immediate vicinity can throw off the readings.”

“That’s true …” Sans murmured, more to himself, his eyes drifting toward the machine that Gaster already thought of as his.

“And it would give you more space to set things up how you like,” Gaster added.

Sans didn’t say anything for a few seconds. He just looked at the machine, a slight crease in his browbone, the face he wore when in particularly deep thought.

“What’s the place like?” he asked at last, snapping his eyes back to Gaster. “I didn’t think there were any more rooms in this building.”

Gaster hummed and shook his head.

“No, not in this building. It’s actually a fair distance away. But I could help you move the T.F. machine there, and you could fill the space as you like,” he replied. “It’s a little room I set up in Waterfall.”

Sans’s browbone shot up so high it almost disappeared off the top of his head.

“Waterfall? You wanna get rid of me _that_ bad?”

Gaster put a hand to his forehead and sighed before dropping his arm back to his side. “Sans, I promise it’s nothing like that. I had just expected that a lot of our work would be collaborative, which is why I assigned you to work here with me. But you’ve quite taken off on your own research, and I thought you might like a more private space to do it. If we do collaborative work in the future, of course you’d be welcome to come back here, or any other time you like.”

Sans paused again. The uncertainty on his face began to fade, and in its place, Gaster saw the beginnings of the same gleam that had grown in his eyes when Gaster told him that he was officially accepted to work at the lab.

“So … it’s just a room?” Sans asked.

“There’s nothing there at the moment, though there are access lines for water and power we could reactivate,” Gaster said with a faint smile. It had been a while since he had seen Sans really happy about something, and he had sorely missed it. “I had it built when I lived in Waterfall, so that I would be able to do some work close to my home. Then I moved here and took everything out, so it became useless. It’s locked, and I’d give you the key, so you’d have full access for whatever you wanted to work on.”

Sans didn’t say anything at first. He glanced around the lab, then at the T.F. machine, his browbone furrowed with a mixture of longing and internal conflict. When he met Gaster’s eyes after a minute of silence, Gaster just smiled.

“It’s entirely up to you.”

Sans hesitated again, his smile low and tight, but the gleam in his sockets just a bit brighter. “You’d really let me take the T.F. machine?”

“No one else is using it,” Gaster replied. He smiled wider, and though Sans looked away, he didn’t need to say anything else for Gaster to get his answer. He chuckled. “We can leave early today and I’ll take you by. If you like it, I’ll help you move the T.F. machine there tomorrow.”

Sans started to say something, then stopped, staring back at Gaster for a few seconds before he nodded. Though he turned away a second later, it wasn’t quite fast enough to hide the childlike glee that flashed across his face.

Gaster smiled wider.

Neither of them spoke after that. Sans went back to his work, and Gaster pretended to focus on his—even if he still had nothing to work on—sneaking brief glances at Sans every minute or so, just to see his wide smile, his bright sockets, the eagerness in every movement he made, the same enthusiasm Gaster had seen on his best days in university, when he came home ranting on about something new he had learned.

Yes. This was how Sans should be. This was what Gaster had wanted so badly to give him.

Maybe the research would have been a success. Or maybe it wouldn’t. It didn’t matter. Sans was happy now, and he definitely hadn’t been happy before. He had been miserable. And who knew how much longer he would have been miserable if he hadn’t spoken up. Who knew how much longer Gaster would have gone on doing his experiments, without a thought to Sans’s pain.

Maybe it would have been a success, if he had given it enough time. But it wouldn’t have been worth it. No matter what the results had been, even if he had shattered the barrier and brought them all the Surface—even if he had gained everything he had hoped for—it wouldn’t have been worth it for a second.

This was his son. And nothing, _nothing,_ nothing in the world, was worth hurting his son.


	16. Chapter 13

**Notes for the Chapter:**

> I must say, it is ... absolutely fascinating seeing all your guesses for how this is going to go. You'll find out very soon ... ;) As always, thank you so much for all your kind words.

It was the first time his dad had taken a day off, not for one of their events, or because Papyrus or Sans wasn’t feeling well, or for anyone else but himself, in more than five years, and when he told Sans he would be staying home from work, Sans wasn’t sure whether to be immensely relieved or ecstatic.

He tried to settle on the latter. After all, his dad had been doing a lot of work lately, and as much as Sans had suffered more for it, he had little doubt it had been rough on his dad as well.

Plus, he had been a lot quieter lately, a lot less productive, and Sans couldn’t help but wonder if he was still wallowing in guilt.

Sans could have tried to tell him that he wasn’t mad. He _had_ tried, once, that first evening when his dad wouldn’t stop apologizing. But after that, he realized it was useless. His dad was going to beat himself up about this for a while, no matter what he did. Maybe that was his way of dealing with what had happened. If past events were anything to go by, he would move on soon enough.

Then again … nothing like this had really _happened_ before, had it?

His dad had never hurt him—definitely not on purpose. The idea of causing either of his sons pain, mental or physical, had likely never even occurred to him, from what Sans could tell. And he had gone straight from that to … could it be called torture when it had a real purpose?

And it _had_ had a purpose. It hadn’t just been for the hell of it, or to make someone talk, or any of the other reasons he had read about humans torturing each other for. It had been for a reason, a _good_ reason, a reason Sans had agreed with. A reason Sans had … pushed for.

He had wanted it. He had agreed with it. He had all but leapt onto that table, ready to be experimented on, if there was even a chance it could help them get out.

But he had changed his mind. He was allowed to change his mind, wasn’t he? And he felt so much better, now that he could just go to work like he had before. Now that he didn’t have to lie down on a table and have his soul poked and prodded and examined and ripped. It had been the right decision to back out. Hadn’t it? No matter what he had wanted. No matter what he had really thought they would be able to do.

If they had kept going, though … could they have really done it?

If he hadn’t decided it was too much, that his dad had gotten too obsessed, that it was too painful—

He couldn’t even figure out what had tipped the scales for him. Sure, it was uncomfortable, but he hadn’t been lying at the beginning. If he had had good reason to believe that the pain would lead to them getting out of here, he would have endured twice as much. It was more than he had expected, yeah, but he could have handled it, couldn’t he?

But his dad …

Was that why he had backed out? Because his dad wasn’t acting like his dad anymore? Because he had Papyrus so worried? Because it was so much harder for Sans to lie there gritting his teeth against the pain when his dad was watching the _readings,_ marking everything down, _smiling_ at the results, rather than giving a damn about his own son?

Was that a good enough reason to back out? For something this important …

If they never got out of here … if they were stuck in this cave for the rest of his life, for centuries after he died … would it be his fault?

No. No, they would get out of here. The king was still collecting human souls, wasn’t he? Sans had heard he already had five. They couldn’t exactly predict when another one would come, but if it had happened before, it would happen again. One day, he would have seven, and they would get out of here. No need for artificial souls. Then they could see the Surface, just like his dad wanted them to. Just like _Sans_ had wanted to.

And in the meantime … he could focus on his own research.

It had only been a few weeks since he last did work on what he was beginning to think of as “The Ripple Project,” but he had never been happier to get back to his work. And as much as he had initially protested, having his own lab really did make things easier, even though he was only there part of the time. The readings were cleaner, and likely a good deal more accurate, and he could set up the room exactly how he wanted, without having to work around the clutter his dad seemed to adore. He could take breaks when he liked—which, in his case, meant not very much—and he could focus entirely on his work without any interruptions, accidental or otherwise.

Of course, it also meant that he was free to invite anyone else to visit, without worrying about them not having a key card or going upstairs to let them in.

And just as expected, a couple of hours after he got to the lab, a shaky knock sounded on the door, and Sans was smiling even before he turned around.

“Come in!”

The knob turned, then paused. A second later, the door creaked open, so slowly he would have thought it was the wind if he hadn’t seen doors open in exactly the same fashion hundreds of times since he was a kid.

A yellow head poked through the door, meeting his eyes and offering a shaky smile before the rest of the body followed. She hunched over a bit so that she looked as short as he was, her arms tucked close to her torso, her eyes flicking around the room as if assessing a war zone. Still, Sans couldn’t stop himself from smiling wider.

“Hey, Alph.”

Even though she was already looking at him, she stiffened, slipping into the room entirely and pushing the door shut behind her.

“H-hi, Sans.” She lifted a hand in a shy wave before wringing it with its twin in front of her. “Sorry, I, uh … got a little lost on the way …”

Sans glanced at his watch and finally noticed the time. 11:15. Right. Hadn’t they planned to meet at 11:00? He shrugged.

“Don’t worry about it. C’mon in.”

She was already inside, of course, and there wasn’t much room for her to get further in, given the size of the lab. But she probably would have stayed within three feet of the door if left to her own devices, and once he spoke, she finally took a few steps further, looking around with eyes wide less with anxiety and more with wonder.

“You w-weren’t k-kidding when you said your dad gave you a p-private lab,” she breathed.

Sans chuckled.

“Yeah, uh … still getting used to it myself,” he replied. “There’s not much here yet, but I’m still moving in. I’ll hopefully have this place decorated pretty soon.”

Alphys hummed, though she didn’t seem to be paying much attention anymore. As usual, the equipment and the paperwork—as little as there was—had caught her eye, and he could practically see the longing rolling off her in waves. His smile softened into something nostalgic and fond.

“Y’know, I actually meant to ask if you’d like to use this place for your own research,” he said, as casually as he could manage, even though Alphys flinched the second the sentence left his mouth. “There’s plenty of space, and if you want, we could even put in an application with my dad and get you—”

“Oh, no no no no, I-I couldn’t, I …” She trailed off, shaking her head so hard her glasses almost slipped off her nose. She adjusted them, avoiding his gaze with practiced skill and wringing her hands closer to her torso. “W-what are you w-working on right now?”

Sans held back a sigh, but smiled anyway, turning back to the rest of his miniature lab with a shrug.

“The T.F. machine, mostly. My dad basically gave it to me, since no one else was using it and it was what I was focusing on,” he replied. He stepped closer to the machine in question. “I’ve actually been looking into some weird readings the machine’s been getting. My dad said they’ve been like that since the beginning, and even Dr. Billington couldn’t figure out why the readings didn’t match up with what her research said they should be. My research, too.”

Alphys wandered up behind him, looking around with the widest eyes he had seen on her face in years. His smile tilted up further as she looked to him at last, more hesitant than she really should have been, given that they had known each other for fourteen years.

“C-can I …?”

He held out his hand toward his desk and the machine, sweeping his arm to motion toward the rest of the lab. “My research is your research. I’ve pretty much hit a dead end at this point, so I’m not even sure if I’ll be able to do anything else with it anyway. But look all you want, you know I’m always open to your ideas, Alphys.”

Alphys couldn’t quite hold back her smile, and with a tiny nod, she scurried forward and started flipping through the papers on his already-cluttered desk.

She had grown a lot since he first met her, but in some ways, she had never really changed. She was still just as eager as she had been when she was ten years old, muttering about her ideas for a science fair project and ranting on about all the latest research and things she had read whenever she came over to babysit. Granted, she spent about the same amount of time going on about anime, and never seemed to notice when Sans and Papyrus slipped away to go start a jigsaw puzzle until she snapped out of her fangirl trance.

But she had been his favorite babysitter—well, tied with Dr. Japer—and he couldn’t pinpoint the exact time when he had shifted from viewing her as an older girl who watched him and his brother to a fellow science nerd, and a friend.

He wasn’t even sure when she had started coming over when his dad wasn’t paying her for it.

She had already been in college for three years when he started, and he had assumed that as soon as she finished her graduate work, she would go on to become a scientist, just like she had always talked about when they were kids. Just like she already _was,_ in his point of view, even if it wasn’t her official job title. She had gotten her bachelor’s, and her doctorate, after that. Top of her class, just as he expected. She could have gotten any position she wanted.

But she never applied for a job.

At first, he thought she was just looking for one she liked. Maybe she was being picky, and he couldn’t blame her for that. But months went by, and then years, and then Sans was getting ready to finish his doctorate and she was still making her living repairing broken technology. It wasn’t a bad living, by any means. But it was far, far below the level of skill she actually had.

His dad would have hired her. He had no _doubt_ he would have hired her, no application, no interview, right on the spot, the second she mentioned it. But she never brought it up, and she brushed aside any attempts by Sans to nudge her into giving it a try.

Just like she had flushed and run off the stage when they tried to announce her as valedictorian at her commencement.

Sans was smart enough to know when he was facing a lost cause. But Alphys had been far too good a friend for far too long for him to give up on her entirely.

“H-have you considered parallel universes?”

Sans’s head snapped up, and he jerked around to face Alphys—where she had apparently moved in front of the T.F. machine, examining the little screen with numbers flashing as the machine itself hummed.

“What?” he asked.

“Parallel u-universes,” she repeated. After a few seconds of silence, she glanced at him, clearing her throat and fidgeting with her shirt. “I-I mean, as an explanation f-for the d-discrepancy in the readings.”

Sans stared at her, the words clicking in his head.

“Parallel universes.”

Alphys bit her lip and shifted from side to side.

“Well, y-yeah, I mean … theoretically, the energy from universes c-close to ours might s-spread and affect the readings from _o-our_ universe. I-it’s hard to say for sure, s-since it’s all s-speculation at this point, b-but—”

“Alphys, you are a _genius_! ” Sans burst, his voice loud enough to bounce off the walls and echo all around them.

Alphys snapped her head back to him, eyes wide, glasses slipping down her nose.

“I … what?”

But Sans wasn’t listening, his mind already running faster than it had moved in weeks, his smile spreading across his face.

“I can’t believe I didn’t think of that!” Sans went on, pacing, unable to keep still with the energy threatening to blow his bones apart from the inside. “I’ve been staring at these readings for _weeks,_ I thought of _everything,_ and you got it in one go. And they called _me_ brilliant. You’re the one who knows how to think outside the box. ”

Alphys just fidgeted again, though she couldn’t hide the shaky smile growing on her face, nervous, yet still pleased. “W-well …”

Sans shook his head and laughed.

“It fits perfectly. It answers everything! Of _course_ the readings wouldn’t fit within the predicted range, if the machine’s picking up the ripples from _other_ universes, too! God, how did I not think of that before?”

“U-um …”

Sans stopped his pacing, paused, then spun around back toward his desk, yanking out several pieces of paper from the closest notepad he could find. “C’mon, I gotta get this down. You up for helping me a little more?”

Alphys paused, as if she couldn’t quite understand what he had said, before he heard her shuffle up behind him.

“I’m f-free all day.”

“Great,” he said, turning his head long enough to flash her a grin over his shoulder. “Then we’re getting ice cream. My treat. Once I’ve got all this written down, we can go eat and start thinking about how we’re going to get started.”

He was already in the middle of jotting down his thoughts before they flew the coop, but he could still feel Alphys’s eyes on him, wide, her breath apparently caught in her throat.

“… we?”

“You said you’re up for helping, right? Or collaborating.” He finished up his current line of thought and turned around to face her in full, smiling at her even as she stared at him like he had completely lost his mind. His smile softened, and suddenly it was so easy to remember when their age difference had been more apparent, and she had been the cool science nerd he looked up to for so many years as a kid. “This is your project now, Alphys. Just as much as it’s mine.”

Alphys swallowed and averted her eyes, her hands clasped in front of her torso, her hands wringing as she shifted her weight.

“T-that’s … you did all the work u-up until now …”

“Yeah, and I’d still be stuck if it weren’t for you,” he replied, without skipping a beat. When she remained silent, he stepped forward to rest a hand on her shoulder, giving it a brief squeeze. “You’re the best, Alphys. Always were.”

Alphys’s face looked like it had spontaneously changed color, but as hard as she tried to speak, she couldn’t manage a word.

Sans just smiled wider and turned around to finish his notes.

Maybe they wouldn’t be breaking the barrier with artificial souls anytime soon. But that was fine. There were things to do here, things to discover, things to learn. Eventually, another two humans would fall, and they would have all the souls they needed to get out. But in the meantime, they were okay. They were happy. And they were moving forward.

That had been enough for his dad for as long as he could remember, and hopefully, soon, it would be enough to make him happy once again.


	17. Chapter 14

**Notes for the Chapter:**

> Nothing to say about this one. ;) But seriously, thank you so much, everyone. I'm so glad you're enjoying this.

When Gaster had suggested that Sans take over the abandoned lab in Waterfall, he hadn’t been thinking that that would make him work even more.

Of course, he had hoped to give Sans the freedom to do what he really wanted—especially after he had pressured him into doing things he _didn’t_ want for so long. He had almost forgotten, in the midst of it all, that Sans was still a workaholic, and giving him the chance to focus completely on his one true passion would just give him more reason to come in early and stay late and skip his breaks. And Gaster wouldn’t even be there to make sure he ate his lunch.

He still came home for dinner, thankfully, if only because Papyrus was sure to complain if he didn’t. But he had often left the house by the time Gaster woke up in the mornings, and Gaster wouldn’t be surprised if he started to sneak out in the evenings as well. Sometimes he would drop by during the day to chat or to grab some more supplies, but the rest of the day, he was gone, out of Gaster’s sight.

But Gaster couldn’t bring himself to say anything about it. Sans was happy, even if he was running himself ragged.

At least he was running himself ragged for something that brought him joy.

Gaster didn’t get any work done on those first days that Sans was gone, though that was hardly a change from when Sans was there. He couldn’t focus on any of his projects, and the king hadn’t sent him a single new assignment. He checked the Core readings—unchanged, as always—and searched the lab for useful abandoned projects—nothing of use—before he sat down at his desk and stared at the blank notebook in front of him as if it might reach out and throw some ideas in his face.

Was this how Papyrus felt on the days he stayed home and had nothing to do? Or was he just used to it since he had graduated, busying himself with housework and shopping so he never got bored?

Maybe this explained the phase he went through as a teenager, spending every minute of his spare time making scrapbooks when Gaster and Sans were otherwise occupied.

The lab certainly needed some organizing, especially those old files. And he could probably do a bit more cleaning. But Gaster wasn’t quite bored enough for that yet.

Besides, he really didn’t feel like looking through the file cabinet when that dusty green folder still sat in the back.

At the end of the first full week since Sans left for his own lab, Gaster found himself again with a day of work, a day of pay, and absolutely nothing to show for it. Dr. Japer had poked her head in once or twice to check on him, but though she offered to have lunch with him, he found himself declining. He was bored, but for some reason, being around his friends didn’t seem any more appealing than anything else.

Before he left the lab, he glanced at his white coat, hanging on one of the chairs where he had left it on the day of that last experiment. Funny, how quickly he had gotten used to wearing it. Funny, He didn’t feel like he deserved to wear it now.

But he hadn’t deserved to wear it as a scientist hurting people with his experiments either.

He reached out a hand to touch it, then pulled back, sighed, and walked out through the lower labs, into the elevator, and across the second floor.

It wasn’t until he stepped outside that he heard the shouting.

His head snapped up, staring at all the monsters to his left, running toward the bridge leading to Waterfall.

Gaster stood frozen. It didn’t look like they were running _from_ anything. None of them screamed or looked behind them as if there were something at their heels, and this wasn’t by far all the monsters in Hotland and the Capital—unless they had already crossed the bridge while he was inside.

But they were upset. That much was obvious. They were scared, they were panicked, they weren’t looking back. Like they were running _to_ something.

He stepped out further, trying to get close enough to catch a snippet of conversation, but no one was talking loud enough for him to make it out. Finally, when a young woman passed him, he reached out and brushed her shoulder with the tips of his fingers.

“Excuse me?” he asked as she spun around to face him, her eyes still flicking ahead of her, as if anxious to keep moving. “What’s going on?”

Her brow furrowed. She stared at him for a few seconds before she shook her head, slow, confused, and a little bit embarrassed.

“I’m sorry, I … Dr. Gaster, I can’t understand what you’re …”

Gaster paused before it hit him in the face. His shoulders sagged, and he resisted the urge to smack himself in the forehead. Instead, he lifted his hands and signed, the movements more clumsy than they had been in years.

HAPPEN WHAT.

The woman blinked, taking a moment to process the signs before her brow rose, and she shook her head.

“Oh. I … I'm not sure, I heard …” She looked over her shoulder, more anxious than before, her eyes following the crowd of people crossing the bridge. “Someone said there was a rockslide. In Waterfall. A few monsters were injured … I’m sorry, I have to go, I have friends in Waterfall …”    

But Gaster wasn’t even listening. She slipped away, and Gaster just stood there, her words echoing in his head as the pieces clicked one by one.

Sans was at his lab.

His _new_ lab.

In Waterfall.

Gaster didn’t notice when his feet began to move, and once he had broken into a run, he didn’t stop.

He must have bumped into ten people in the first few minutes, but he never stopped to excuse himself as he always would have before. He couldn’t stop. He couldn’t think. He had to keep going, get there faster, why couldn’t he move faster, he could run faster than this when he was younger, _why did he have to be so old—_

He didn’t know where he was going. He followed the crowds of people already flocking ahead of him, Waterfall was large, there were plenty of places that woman could have meant, but he had to find Sans, he had to make sure …

Make sure …

Gaster’s legs burned, his chest ached, but he ran faster still.

The crowds got thicker, and it got harder and harder for Gaster to move through them. He murmured apologies no one understood, and for once, actually thanked his genetics for making him tall enough to see over quite a few other monsters. Even though he rarely left the lab, nearly everyone knew who he was, and they stepped aside when he tried to slip through, even though they had no idea why it was so urgent.

At last, he reached the front, and it took his eyes several seconds to recognize exactly where he had ended up.

It was … the clothing shop.

The little shop where he had bought all the boys’ clothes when they were young, before they could search the dump for clothes that fit their own sense of style. It was small, the selection had never been great, but they had some of the best customer service Gaster had ever seen, and they always made sure anything they sold had been well-cleaned and patched up. Perhaps their products would never look new, but they would hold up. Through all their rambunctious playing, Sans and Papyrus had rarely torn anything they wore.

It was a family that owned it. What was their name? Signa? He thought that was it. They were sweet. They had children. Grown children now, they had been teenagers when Sans and Papyrus were toddlers. Gaster hadn’t been there at all in at least three years.

And … their shop was gone.

He could still make out a few parts of it—the material that had made up the walls, the front door, pieces of the roof. But they were all scattered on the ground, knocked off to the side, and the rest of the shop had been completely crushed by the rocks that had fallen from the ceiling above.

The _stone_ ceiling. The mountain itself, a good ten yards above their heads.

Where a large dent had now been carved out, uneven and covered in the same dust that spread across the ground.

A cave-in.

Small, only affecting this one area, but … he knew the word. He had seen diagrams, pictures, he knew what they looked like.

The mountain had caved in.

People were chattering on either side of him, but Gaster couldn’t make out a word of what they said. He forced himself out of his stupor, looking right and left, searching for even a sign of a white bony head, why did Sans have to be so _short,_ he could be anywhere in this crowd, maybe he wasn’t here, maybe he hadn’t heard about it, maybe he was still safe in his lab, maybe he would come home just as he always did and everything would be—

Gaster’s eyes fell on another group of people, behind the main crowd. He hadn’t noticed them before, but they were dressed in official-looking uniforms. Not the Royal Guard, but … what was the emergency medical team called again? He knew they were healers, at any rate, dressed in pale green outfits, each of sitting in front of another monster, their glowing hands resting on the injuries as they forced their own magic in.

Then he saw him.

Far to the back, a healer crouched next to him, the glow in their hands fading as they finished what looked like a long session.

Gaster didn’t even notice his feet moving until he was halfway there.

“Sans!”

Sans’s head snapped up, searching for only a second before he found the source of the voice. “Dad?”

The healer stepped away just in time for Gaster to drop to his knees in front of Sans, putting his hands on his shoulders and looking him over from head to toe, ready to gather up his magic at the smallest sign of a crack.

“Where are you hurt? Were you under that? Is anything broken, what’s your HP, here, let me—”

“Dad, I’m fine, I’m fine,” Sans cut him off, leaning back so far he almost toppled off the rock he had been using as a makeshift chair. He looked to the healer, giving them a nod before they slipped off to help the others. Then he turned back to Gaster. “I was only under there for, like, a minute. They got me out right away, it barely hurt anything, I’m okay.”

But Gaster was still trying to look, even as Sans tried to shove him away, even though he was making this more than difficult, why couldn’t he just let him _look_?

“Dad,” Sans tried again with an irritated sigh. “Dad, c’mon, they already healed me, I don’t need—”

“Please, Sans,” Gaster cut in, looking down at him, his eyes as pleading as his soul.

Sans looked at him, pausing. Gaster stared back without a word. But words weren’t needed. Sans huffed another sigh and sat up straighter on the rock, letting his hands fall to his sides.

“Okay. Go ahead.”

Gaster didn’t need to be told twice.

He checked him over, his magic already flowing out of his hands before he had a good reading on his HP. His soul twisted at the familiar motions, though he did his best not to let his magic flicker at the thought. He had been doing this far too much lately. More than he had done even when Sans was little and spent half his time bumping into furniture because his depth perception was off.

Sans was right—as he usually was. The healers on site had already taken care of any damage. There wasn’t a scratch on him, and his HP was maxed out. But Gaster checked him anyway, from head to toe to soul, searching for anything they might have missed. Any damage that might lead to problems later on.

There was nothing.

But every time Gaster glanced over Sans’s shoulder and saw the fallen pile of rocks where a line of shops had once stood, he found himself wanting to check again.

Sans allowed it for a few minutes, but finally he slipped out of Gaster’s grasp and got to his feet, walking over to where the rest of the crowd had gathered. Gaster tried to stop him, but his words came out as useless as they were to any of the hundreds of monsters who had no idea what he was saying. So he followed his son, closer to the rockslide, toward where two members of the Royal Guard were ushering away the crowd.

The smaller Guard seemed more timid, quiet, while the taller one, towering above even Gaster with her long thin legs and antennae, held a wide stance, arms spread out to her sides, somehow plenty imposing even without proper tape to hold everyone back.

“Everyone, if you could please just—oh!” As Gaster and Sans slipped through the last row of the crowd, she stopped and turned to him, blinking. “Dr. Gaster.”

Gaster looked over her shoulder, then back to her, lifting his hands even though his mouth opened on reflex. HAPPEN WHAT.

It felt so stilted, so inadequate, he had seen monsters use sign language to express the most complex of thoughts and feelings, he had spent more than two millennia years unable to make anyone understand him with words, so _why couldn’t he just get out anything more than these clumsy hand motions—_

“We’re … we’re not sure,” the shorter, more nervous member of the Guard replied at last, jerking Gaster’s attention back to them. “Some of the witnesses say there was a bit of noise overhead for about ten minutes before the collapse, but …”

Before Gaster could even think of what to say or ask, Sans had slipped in front of him, standing as tall as his minimal statue would allow, browbone wrinkled in concern.

“Was anyone else hurt?”

The two Guard members exchanged glances. The taller one turned to Sans. “We’ve sent a few people off to special healers due to their injuries, and there were about eight healed here, but there were no casualties, as far as we know.”

“Good.” The line of Sans’s shoulders softened. “Anything I can do?”

Gaster stiffened, jerking his head to face him. “Sans, you were just—”

“I’m fine, Dad, I can help,” Sans cut him off, sparing him only a glance before he looked back to the Guard members. “What can I do?”

The Guard members exchanged another look. The smaller one flicked their eyes to Gaster, then back to Sans.

“Some of the other monsters have been helping look through the wreckage,” they replied, looking over their shoulder at the five or six people who were digging through the pile of rocks. “It looks like the shop is … completely destroyed, but the Signa family kept a lot of their personal belongings in there.”

Sans nodded. “I’ll go help.”

He walked off without a pause, but Gaster started after him, his soul pounding so hard in his chest he thought it might choke him.

“Sans, you shouldn’t go near there, what if there’s another collapse?”

“I’ll keep an eye out!” Sans called over his shoulder, barely sparing him a glance. “You help keep everyone else back so we have room to work, okay?”

Gaster stopped, his hand already halfway in the air. “Sans …”

“Actually, Dr. Gaster, if you wouldn’t mind, that would be a big help,” the smaller Guard member broke in, with a slightly nervous smile.

Gaster turned to them, glancing back at his son, already crouching in front of the rubble to dig out anything he could salvage for the family. Gaster’s hand fell back to his side, and he gave a small, resigned nod.

ALRIGHT.

It was really the worse possible job to assign someone as socially-awkward as he was, but apparently the fact that he was so well-known and well-liked among monsters made people more likely to listen to him than two Guard members whose names they didn’t know. The crowd didn’t quite dissipate, but it backed up, and over the course of an hour, more than half of those who had gathered went home—or perhaps to visit those still being healed, to give their sympathies and help to those who could really use it.

He worked for another hour after that, before Sans finally returned to him, saying that they had collected all the items that would be salvageable—not very many, going by the disappointed look on his face. Gaster just nodded while Sans said his goodbyes to the other volunteers and the two Guards. Then the two of them started back through Waterfall toward Hotland, ready to reassure Papyrus, probably still bustling around in the kitchen, unaware of all that had happened.

Several times, Gaster tried to speak, but his voice always died in his throat, and finally, he gave up, staring at the ground in front of him as he and Sans walked in silence.

This had never happened before.

They had lived underground for over two thousand years now, and there had _never_ been a rockslide like this.

Of course, geological phenomena were hard to predict, and that was with all the information. They had no idea what was going on on the surface. Had the humans settled near the mountain? Had they settled _on_ the mountain? Were they building something up there, something that put a lot of pressure on the side of the mountain, enough to weaken it?

Were they going to keep building?

Was it going to get worse?

What if it happened again, somewhere else? What if it happened somewhere more populated? What if there was no notice, just as there didn’t seem to have been this time?

What if Sans was there, too? Or Papyrus?

What if they were a good deal closer to the collapse, and there weren’t healers so close by?

What if … it was too big for any of them to escape?

They were trapped down here. They could run away from a smaller collapse, but if something happened aboveground and the entire _cave_ collapsed? It was unlikely, certainly, but if a small collapse had happened, a larger collapse could as well. And they couldn’t cross the barrier. If something happened to make this cave uninhabitable, they were stuck.

They would die.

 _Everyone_ would die.

He clenched his teeth and shook his head, ignoring the concerned look Sans gave him. No, that was ridiculous. They had been down here for centuries. The mountain had held them up so far, hadn’t they? And it took more than construction to collapse an entire _mountain._

But …

Most mountains weren’t hollow, as far as he knew. Most mountains didn’t have this much space inside them, space not taken up by magma or anything else that would keep them stable. Hollow structures, especially if they weren’t _designed_ to be hollow, were far less stable. Far more prone to collapse.

They had been down here two thousand years. Two thousand years, and this mountain had held.

But it couldn’t hold forever.

And if the humans _had_ settled nearby, if they were doing something to speed up the process …

They had stolen everything from them. _Everything._ They had taken the sun and the sky and the stars and the rain and the grass and the trees, they had stolen everything Gaster had once taken for granted. They had shoved them under this mountain, and now they were going to take that away, too.

They were going to kill them.

Not just some of them, not just _everyone that had been murdered in cold blood in that damned war_.

They were all that was left of monsterkind.

And if they remained trapped down here, if the mountain, even part of it, collapsed while they were still down here …

Gaster glanced over his shoulder, back toward the rockslide, now out of sight. Then he looked at Sans. He could still see him making his way through the crowd, offering his help to salvage things from the remains of the shop. So eager to help. Just like his brother. Just like both of them had been since they could talk.

He had been so willing to sacrifice his own comfort to get them out of there. He had been _so determined_ that their work would break the barrier, that they would finally be _free,_ without waiting for another two souls to fall.

Then he had changed his mind.

But … it had been for a good reason. He hadn’t just changed his mind on a whim, he had changed it because he was in _pain,_ because it had been worse than he expected, because Gaster had stopped paying attention to how the experiments were affecting him. He had had every right to change his mind.

And Gaster had no right to stand here thinking for even a _second_ that …

He looked at Sans, his son, walking at his side, his head still low. Probably still thinking about the Signa family. Probably still thinking about other ways he could help. That was what he always wanted to do, wasn’t it? Help people. Sans would do whatever he could to help those around him. Sans and Papyrus both.

None of this was his fault.

He had done far more than he ever should have.

Gaster closed his eyes, took a deep breath, and shook those thoughts away.

But as he opened them again, as they crossed the bridge from Waterfall to Hotland, he looked around him, at the walls of the cave, at the paths leading out behind him and ahead of him, stretching out far past his line of sight.

And in two thousand years, the underground had never looked so small.


	18. Chapter 15

Gaster had been working alone in the lab five days a week since his sons started school. Sans had only worked with him for a couple of months, actively, and before that, aside from brief visits by his colleagues or his sons or even the king on rare occasion, Gaster had done all his work by himself.

Which was why it made no sense that the lab should feel so quiet now that Sans was gone.

He had never realized how much of an echo there was in the tiny room, despite the amount of clutter there to absorb the noise. He had never realized how much he muttered to himself, how much he paced, how loud the clock on the wall ticked as each second passed by.

He had never realized how easy it was to get sucked into his own thoughts, so deeply and so quickly that he barely even noticed when it happened.

Sans came by from time to time, to gather supplies, to check in on him, to chat. But today, he had left after breakfast to go to his new private lab in Waterfall, and Gaster hadn’t seen him since. He had almost everything set up to work there permanently, and he had migrated there far more quickly than even Gaster had imagined he could.

He had joked, half-heartedly, that Sans seemed very eager to get away from him, but Sans had just rolled his eyes, shook his head, and flashed him a grin.

Maybe it was better that Sans wasn’t here, though. If he had been here, he would have been worried. If he had been here, he would have noticed that Gaster had stopped working on any of his projects, even small ones, and had spent far too much time pacing around the lab, so engrossed in his thoughts that half the time, he forgot to take the same lunch break he had so insisted on for Sans early on.

He was ridiculous. Completely ridiculous. Yet he couldn’t shake the thoughts that seeped into his head, or the images of Sans being crushed by rocks falling from the ceiling, or the rush of terror that shook him so hard he could barely breathe.

He couldn’t shake the thought that it could have so easily turned out worse.

He couldn’t shake the thought that if he had continued with his work, with his project, _if he had broken the barrier,_ then Sans wouldn’t have been in danger at all.

That was ridiculous in itself, of course. Even if he had continued, it would have taken longer to complete the research, and even longer to actually create the artificial souls, no matter what method he went with. He would still be working now. So it wouldn’t matter. Whatever _would_ have happened, Sans _had_ been in Waterfall, and he _had_ been caught under the rockslide—at least in part—and he _had_ come out with his life intact.

He couldn’t spend all his time focusing on “what if”s.

Even if he had spent almost his entire career doing exactly that.

Sans called at around four in the afternoon, saying that he was heading home early and asking if Gaster wanted to join him and Papyrus for a nice family meal. Gaster had every intention of saying yes. Of course he should say yes. He loved spending time with his sons, and he hadn’t been doing it much lately, and besides, he had nothing pressing to work on. Nothing _at all_ to work on. The only sensible answer was yes.

But Gaster still heard himself saying that he wouldn’t be able to make it home in time, and that he probably wouldn’t be back until late.

Sans was disappointed, as much as he tried to hide it. Gaster hated himself for that. But he still couldn’t manage to take it back before they both hung up, and he was left once again standing in his lab, cluttered and cramped and far too empty.

After several minutes just standing there, Gaster put down his phone, sat down at his desk, and picked up a pen.

There was nothing to work on. Nothing he could write down, no ideas rushing into his head for him to plan out. His mind was as empty as the lab, and even the abandoned projects now tucked neatly away into drawers in one corner looked just as boring as they had a week before.

Gaster wasn’t sure how long he had been sitting there when his eyes first drifted to the file cabinet.

And the bottom drawer, untouched since he had slammed it shut weeks before.

His hands rose to the edge of the desk, as if to push himself up, already leaning his body toward the cabinet.

Then he stopped and forced himself back down into the chair.

No. He had made his decision, and it was the _right_ decision. He couldn’t hurt his son. He couldn’t put him through any more suffering than he had already endured—suffering he shouldn’t have had to endure in the first place. Nothing was worth that. He was a scientist, yes, but first and foremost, he was a father. A father who had a duty to protect his children.

But he couldn’t protect them.

That rockslide … how was he supposed to protect them from that?

If there were more accidents like that, what could he do to keep them safe? If the mountain finally destabilized under the strain of hundreds of people living inside it for centuries, what could he do, then?

If their only home failed them, if the barrier still stopped them from leaving …

Everyone would die.

His sons right along with them.

And even if nothing else happened … how long would it be until the king managed to break the barrier on his own? How long would it be until the next human fell, and another after that? It might be decades. It might be centuries. After all, it had been more than thirty years since the last one. What if the humans had realized that there was something dangerous about the mountain? What if they had put up precautions against it? What if no more humans fell?

What if they were trapped down here for the rest of their lives?

They would never see the sun. Never feel the grass or the wind, never see the sky, all they would ever know was this _cave_ and even if they never knew what they were missing out on, even if so many monsters alive today had no idea how bad they had it, that didn’t change anything. Even in his most desperate moments, even when he was determined that he would break the barrier, one way or another, he had still assumed that it would be done eventually, whether he did it himself or not.

He hadn’t considered that that might not be the case. He hadn’t considered that there was anything threatening them while they were stuck down here.

Gaster put his hand to his browbone, letting out a long, heavy sigh.

He wanted out. More than ever since the end of the war, he wanted to get the hell _out_ of this place. He just wanted to live safe and happy on the surface with his sons, was that too much to ask? He didn’t want to be stuck down here anymore. He didn’t want to have to worry about the cave collapsing on top of them, he didn’t want to have to think about everything he could never give them, no matter how hard he tried, he didn’t want to have to choose between hurting one of his sons temporarily and leaving them both stuck down here until the last three skeletons in existence finally died of old age, _he just wanted everything the humans had stolen from them_ —         

A knock came at the door, harder and a bit more energetic than usual. Gaster sat up—why in the world would Sans knock before coming in, Gaster had told him that this was still a shared lab—but kept his eyes on his desk, tugging a few papers in front of him, as if to pretend he had actually been doing something.

“Come in.”

The door swung open, and it took only a few seconds for Gaster’s distracted mind to notice that the footsteps clunking into the lab were definitely not Sans’s.

In good part because Sans never wore boots.

“Hello, Dad!”

Gaster lifted his head, slowly, his sockets already wide before they fell on the beaming face of the skeleton standing near the door, holding what looked like a picnic basket in both hands.

“… Papyrus?” Gaster managed. “What are you doing here?”

Papyrus adjusted the basket in his hands and stepped closer. He was still smiling, but there was something sad in his eyes.

“Well, you seemed very down lately, and Sans said you were going to work late tonight, so I thought I’d come by and bring you some dinner to cheer you up.” He held the basket up higher and smiled wider. “And I made your favorite! Nacho casserole! I still don’t know why you like it so much, it’s very unhealthy, but this is your special dinner, so I made it the best I could.”

Gaster looked at the basket as Papyrus set it down on the only spot of the table that wasn’t covered in papers. His shoulders fell, just a bit, and he felt his eyes soften and his mouth curl up at the corners.

“Thank you, Papyrus.”

The sadness vanished from Papyrus’s sockets as if it had never been there. He beamed. “And there’s dessert, too. Chocolate lava cake! Your other favorite!”

Gaster nodded, his chest just a little warmer. “That’s very kind of you.”

Even though Papyrus’s smile already stretched all the way across his face, it somehow widened further.

“Would you like me to stay and eat with you?” he asked. “I already ate mine, but I could sit here and we could talk.”

Gaster opened his mouth, then paused as his earlier thoughts came creeping back in. His smile slipped. Papyrus tilted his head and frowned for a moment before smiling once again, hopeful.

“Or … maybe I could help you with something! Sans said a lot of the stuff he did as an intern was fetching things, and I am an excellent fetcher!”

“Indeed you are,” Gaster replied, unable to hold back the slight, fond smile curling his mouth. He shook his head. “Thank you, Papyrus, but I’m fine. I just …”

He trailed off. He knew it didn’t sound convincing, and that was only confirmed when Papyrus took a step closer, his browbone furrowed.

“You’re not fine, Dad,” he said. “Sans does that, too, say he’s fine when he’s not. But it’s not good. You should say what’s upsetting you and then you’ll get it out and it won’t be inside you anymore.”

Gaster looked at him. Just looked at him, _really_ looked at him. He didn’t care what anyone had said about his son. Papyrus was as brilliant as any of them, more so, even if it wasn’t in the same way. Even if hardly anyone could understand it.

Before he could stop himself, Gaster found his mouth opening once again.

“Well … I suppose something has been bothering me.”

In under a second, Papyrus’s whole face was shining as bright as the lights overhead, almost as bright as Gaster remembered the sun.

“I knew it! What is it?”

Gaster hesitated yet again, his gaze shifting away. “You see … Sans was helping me with some experiments. Some very important experiments. Some experiments that … we hoped … we _believed_ … might break the barrier.”

“Break the barrier?” Papyrus asked. His smile had slipped again, his brow furrowed in the same innocent curiosity he had worn when he was just a toddler. “So we could … go to the surface?”

Gaster sighed and nodded.

“Yes. These experiments were the only thing we could think of, we hadn’t tried anything in a very long time, but this … well, I had given up, but your brother encouraged me.”

“He’s good at that,” Papyrus replied, smiling again.

Gaster’s mouth twitched, even though he didn’t really feel like smiling. “You both are.”

Papyrus kept looking at him, waiting, eager and expectant. When Gaster didn’t reply, his smile fell again, just a bit, and his head tilted to the side.

“So … are the experiments not going well?”

Gaster paused. He shouldn’t be talking about this. Not with Papyrus. Sans hadn’t wanted Papyrus to know about this, and Gaster had agreed. He shouldn’t have involved one of his sons in this, and Papyrus … at least Sans had understood what was going on, enough to avoid letting it get to him. But someone as gentle and sensitive as Papyrus …

“They were going well,” Gaster went on, almost without realizing he was speaking. “We … had learned a good deal, but …”

He trailed off and rubbed the bone between his eye sockets, tilting his gaze toward the wall.

“Sans … wasn’t able to handle them. They were … unpleasant for him, and they were hurting his HP.”

Papyrus didn’t reply, but Gaster could feel his stare. He could feel the wide, concerned eyes that followed his each and every moment. The eyes that saw far more than anyone knew.

“So … we stopped,” Gaster finished. He let out another breath and shook his head. “And … I suppose I’ve been upset because we weren’t able to continue this work. Sans’s soul—both of your souls, I should say—are unique, due to the nature of your creation, so I couldn’t just ask any monster off the street to volunteer to be a test subject. I couldn’t even do them myself. And with Sans unable to continue … I was very hopeful that we could really do this, and now …”

He didn’t say anything else. There was nothing else to say. He stared at the wall as if the wall might have answers, as if _anyone_ might have the answers. As if anyone could tell him what the hell he was supposed to do when he couldn’t protect his sons but he couldn’t hurt Sans again and there was no way to do one without doing the other and all he wanted was for them to see the sun before they were old and crazy like him and—

“I could do it.”

At first, the words didn’t even register in Gaster’s head. They sounded like gibberish, like he imagined his own voice must sound to everyone else’s ears. He stared at the wall for several seconds longer, then finally turned to face Papyrus.

Papyrus. His son. Who was looking at him exactly like he had at four years old, offering to help Gaster cook a difficult dinner.

Gaster blinked, a rare, awkward gesture, before his browbone began to furrow. “I’m sorry?”

“I could do it,” Papyrus repeated, and this time, Gaster heard it, clear as water, without a hint of doubt. “I could … do what Sans was doing.”

Gaster just looked at him. His mouth open, his sockets wide even as his bad eye refused to open all the way. Papyrus fidgeted, but stood up straighter, prouder. Eager to assist.

“You said both our souls are unique, didn’t you? So that means mine is, too.”

Even though his mind had started working again, it took Gaster almost half a minute to remember how to speak. He shook his head even as his words failed to come out, his hands clenching at his sides as he wondered why in the world he had ever thought it would be a good idea to bring this whole mess up.

“Papyrus … your brother didn’t continue because the experiments were hurting him.”

“You said they were hurting his HP,” Papyrus replied. “But … I’ve always had high HP. Really high HP. Remember when we went to that doctor when we were little, and she said I had HP in the ninety-eighth percentile?”

“You remember that?” Gaster murmured, more to himself, though Papyrus heard him and nodded, smiling more.

“You never told me what percentile means, but I know it means I’ve got really high HP.”

Gaster didn’t say anything, but he didn’t need to. It was true enough. Sans had fairly average HP for an adult monster, but Papyrus … he had been exceptionally hardy ever since he was a child. His attack and defense were better than average, as well. With such high stats, Gaster had once thought Papyrus might want to work for the Guard, but by his fifth birthday, he knew that would never happen. Enthusiasm aside, Papyrus was far too gentle to do any sort of job that involved fighting.

But he could handle damage. He could handle a _lot_ of damage, without risking his life, and his pain tolerance was just as impressive. Injuries had never bothered him as much as Sans. And he was so eager to help, a different kind of eager than Sans had been, Sans had always been enthusiastic about science and research, enough to rival Papyrus at times, but Papyrus was eager about nearly _everything,_ and helping others, in however small a way, was—

No. No no no no _no._

He was _not_ thinking that. He could _not_ think that. This was _Papyrus,_ he didn’t know anything about the research, he didn’t know what they would be doing, Sans had had some idea, at least, but Papyrus didn’t even—

“So I could do it,” Papyrus went on, snapping Gaster out of his reverie. His smile stretched all the way across his skull. “I could do the experiments so Sans doesn’t have to. Then we could finish the research and break the barrier, like you wanted!”

Finish the research.

Break the barrier.

If he broke the barrier …

His sons would be safe. Even if the Underground collapsed, they would be safe. No more digging through the garbage dump for things they wanted or needed, no more hoping that the Core remained as stable as it was now, no more putting ceilings on their dreams when their dreams should reach the stars.

They could see the sun.

He could barely remember the sun, and they would be able to _see_ it.

It wouldn’t take long. A while, but not _that_ long. He had already done a good bit of research with Sans, and with Papyrus, maybe he could work faster. Maybe he could get more information. Papyrus would recover more quickly, and Gaster wouldn’t be so worried that he would get hurt too badly, and he _wanted_ to help, he had _offered_ to help, it wasn’t like he was forcing him into it or keeping him stuck like with Sans.

This had been too much for Sans. But it wasn’t too much for Papyrus.

Gaster looked at his son, his precious son, looking at him with wide, bright sockets, and felt something slip within him, his shoulders dropping as a tension he hadn’t even noticed slipped away.

“That … would be very helpful, Papyrus,” he said, the words falling from his mouth as if they had pulled themselves through his teeth. “Thank you.”

Papyrus broke into the widest grin Gaster had seen on his face in weeks, holding his head high and putting his hands on his hips.

“Of course! I am very good at helping!”

Gaster nodded, a vague, thoughtless motion. He stared at the floor as his browbone twitched and his thoughts crashed and rebooted a dozen times over.

“I don’t think you should tell Sans about this, though,” he added, his head snapping back up so fast his neck ached.

Papyrus’s beaming grin fell, and he tilted his head to the left.

“Why not?”

Gaster looked away from him. It was far, far easier to think when he was staring at the wall.

“He … Sans … wants to help very badly,” he said, forcing his thoughts into some semblance of organization. “But it hurts him too much. He’s not strong enough.”

When he glanced back, he found Papyrus’s eyes fallen to the floor, his browbone raised, his arms limp at his sides.

“That’s why he was hurting before,” he replied, as much to himself as to Gaster, a good deal quieter than his normal tone. “That’s what he didn’t want to tell me.”

“He didn’t want to worry you.” Papyrus looked up, and Gaster forced himself to hold his gaze as his eyes softened. “Though I understand it had the opposite effect.”

Papyrus fidgeted again, gripping the bottom of his shirt as he looked up again.

“I don’t want to lie to Sans.”

“You don’t have to lie to him,” Gaster said.

Papyrus’s browbone furrowed. “I just have to not tell him the truth.”

Gaster opened his mouth, then closed it. There was nothing he could say to that, and Papyrus knew it just as well as he did. He went silent. Papyrus huffed a nervous sigh.

“I don’t like this, Dad.” He shifted his weight and glanced from side to side. “Sans didn’t tell me the truth before and it just made me even more worried. If I don’t tell him the truth he’ll just get worried about me and then we’ll all be worried about each other and it will just be one big pot of hot steaming worry.”

He looked at Gaster with wide, helpless eyes, and Gaster had to look away again, curling his hands into fists before letting everything out in one long breath.

“I understand how you feel, Papyrus,” he said, as genuinely as he felt. He lifted his head. “But … I think it would make Sans feel even worse to think that he couldn’t handle these experiments and you could. He wouldn’t want you to go through any sort of pain. That’s why he didn’t want to tell you before.”

Papyrus didn’t say anything. Gaster took a careful step closer, his hands out in front of him, palms toward the ceiling.

“But if I can finish these experiments, we might all get out of here.”

Papyrus fidgeted a little more, then stopped. His eyes turned to Gaster. His mouth pressed into a thin line before it relaxed. “We could go to the surface.”

“Yes,” Gaster replied with a soft smile. “You could get that car you dreamed about.”

“And Sans could see the stars,” Papyrus went on, more to himself than to Gaster. He tilted his head to look at the ceiling. “He always wanted to see the stars. The real ones, not just pictures.”

Gaster nodded as his breath slipped out again.

“Yes. But we can’t do that unless we find a way to break the barrier, and I don't think Sans would want us to continue if he knew you were taking his place.”

Papyrus looked at him. He looked away. Back to him, and away again. He shifted his weight from side to side, even though Gaster could see in his eyes that he had already made his decision.

“… alright,” he said. “But just for a while. And if Sans gets too worried, we stop.”

The last of the tension in Gaster’s soul faded, and he barely held back the tight, bittersweet smile that threatened to curl his mouth. He nodded one more time.

“Yes, Papyrus. Of course.”

He would be careful. He knew what to expect this time—he knew what was and wasn’t necessary. He knew what precautions to take. And Papyrus was stronger. He could handle more without suffering the same effects.

He was willing. Maybe he wasn’t quite as informed, but he was definitely _willing._ If there was one person who could rival Sans’s enthusiasm, even if he had little idea what he was enthusiastic _about,_ it was Papyrus.

Papyrus wouldn’t back out. Papyrus would stick with it for as long as was needed.

He would be the one to help Gaster finish his research.

It wouldn’t be pleasant. Gaster knew that. He knew that Papyrus would suffer. _Papyrus_ knew he would suffer. And it wouldn’t be easy to hide any of this from Sans. No easier than it would be to face the music when the truth finally came out, as Gaster knew it eventually would.

But it would be worth it. He had to believe that it would be worth it in the end. Any amount of suffering Papyrus had to endure would be far outshone by how happy he would be when they finally saw the surface, when he finally got the car he had wished for, when Sans got to go outside and look at the real stars.

When all three of them could sit together and bask in the sunlight.

They would get out of here. They would be free and safe and happy. They would get everything that Gaster had ever wanted to give them. He would make sure of it.

One way or another.

**Notes for the Chapter:**

> wisepuma23, is this what you wanted? ;)


	19. -13

**Notes for the Chapter:**

> So ... how'd you like that last chapter? ;)
> 
> I'm so sorry. Here are some babybones to make it up to you!

Daddy was late again.

Sans was used to this by now. Daddy had warned them, after all, that since they were back in school and wouldn’t be in the lab with him all day, they would probably be by themselves for a little while in the afternoon.

Well, not by themselves. All their neighbors knew them, and even though Sans and Papyrus didn’t have an official “babysitter” most of the time—except Alphys, when she had time—they all checked in on the boys at least once every twenty minutes. If Daddy wasn’t home by dinner, one of their neighbors would take them over to their house to eat, and on the very rare occasion when Daddy wasn’t home by bedtime, Mrs. Drenton would come by to tuck them in and read them a story.

It was ten minutes until the usual time Sans and Papyrus went to bed. Daddy wasn’t home. And Sans was reaching for the phone to call him and say goodnight before Mrs. Drenton arrived.

“Not yet.”

Sans looked up at his brother, but Papyrus hadn’t taken his eyes off the door.

“It’s 8:50, bro,” Sans said, his finger hovering over the keypad.

Papyrus shook his head without looking away.

“Not yet,” he said, his browbone set, his mouth pursed into a thin, determined line. “He said he’d be home tonight. He told me, before we left for school. He said he was finishing up a big project today, but he’d be sure to tuck us in tonight to make up for it. And tomorrow we’d do something fun. All three of us.”

Sans fidgeted. He didn’t want to tell Papyrus Daddy wasn’t telling the truth. Daddy didn’t _lie,_ but … sometimes he didn’t think about what he was promising before he promised it. Sometimes he promised things he wouldn’t be able to do.

He wished Daddy would not promise anything at all instead of promise things that weren’t true.

But Papyrus knew Daddy just as well as he did. Even if he was more “optimistic”—that was a good word, Alphys had taught him that word—than most people, he wasn’t dumb. He wouldn’t believe it unless there was a good chance.

Still …

Sans waited. Papyrus waited, staring at the door while the clock ticked away in the background.

8:56. 8:57. 8:58.

Then Sans heard the footsteps on the porch outside.

The lock clicked, and the door opened, and Papyrus shot forward so fast that Sans wondered if he had somehow learned to teleport.

“Daddy!”

Daddy closed the door behind him, and even in the dim light Sans could see the way his body slumped, his eyes half-open, his movements slow. Long day, then. And he probably hadn’t slept very well last night.

Then again, Daddy didn’t seem to have slept well for a while now. Not since he started that new project, anyway.

But even though Papyrus must have noticed that he was barely holding himself up, he still threw his arms around him and hugged him tight enough to crack his ribs. Daddy stiffened, then looked down, his sockets taking a moment to focus before his browbone rose.

“Hello, Papyrus,” he said, his voice as tired as his face. He looked up. “Hello, Sans.”

Papyrus opened his mouth, like he might say something, but instead just stepped back, beaming so wide the smile barely fit on his skull. Daddy smiled back, very small, very tired, but when he turned that smile to Sans, Sans didn’t care what it looked like. Daddy was home. He had kept his promise. Papyrus was right.

Sans didn’t like being wrong, but it was okay if Papyrus was right.

Daddy walked forward, wobbling with each step, and Sans and Papyrus stepped aside to give him room. He was even slower than he usually was at the end of the day, and he didn’t seem to know where he was going. He stopped just in front of the couch, facing the kitchen. He stood there for a long moment, not moving, not talking, perfectly still.

Then he collapsed face-first on the couch, his whole body limp.

Sans froze, and for a second, just a second, he thought Daddy had fallen down. One of the kids at school had talked about it, what it looked like, no, no, Daddy was kind of old but he was _okay,_ there wasn’t anything wrong with him, he was fine, he was—

Sleeping.

Papyrus had moved closer and was poking him in the face, a habit he had never really kicked from when he was a toddler. Daddy shifted, but didn’t wake up. Yeah. He was just asleep.

On the couch.

With his legs still on the floor.

And all his work clothes on.

“He looks really tired,” Papyrus said, apparently having poked him enough.

Sans stepped closer, tilting his head to peer around at Daddy’s face, smooshed into the cushions. “Yeah.”

Papyrus looked at him. “Maybe we should take him to bed?”

“How?” Sans asked, even though it sounded like a good idea. “He’s really heavy …”

“But we’re really strong!” Papyrus replied, grinning.

Sans hummed. “Yeah …”

They looked at Daddy for a few more seconds, then back to each other. Then they each gave a slow, decided nod.

Sans went to his right side, and Papyrus to his left. They had to crawl on the couch to get a good grip under his arms, but finally they managed to drag him onto the living room floor. It was easier after that, at least until they got to the stairs. The stairs were the hard part. They had to pause a few times to catch their breath, and they came close to bumping Daddy’s head against the railing or the steps several times. But Daddy never woke up. He was a heavy sleeper, but usually not _that_ heavy.

By the time they reached the top of the stairs, Sans had never felt so tired. His legs wobbled and threatened to collapse under him, but Papyrus lifted Daddy a little more, and Sans did the same. If his brother wasn’t going to give up, neither would he.

Still, his legs felt like jelly, and his arms hadn’t hurt this bad in all his life. He turned his head toward the first door in front of them, already open, just as he and Papyrus had left it earlier when they came out.

Papyrus started forward, but Sans didn’t move. Papyrus turned to him with a furrowed browbone.

“Sans?”

“We can just put him in our room,” Sans managed, his breath coming in and out so hard he thought he might choke on it. “The bed’s big enough.”

Papyrus looked down the hall, a couple of doors to his right. “But his room’s right there.”

“Yeah, but the floor’s all covered with stuff. It’ll take forever to get him to the bed.”

Papyrus opened his mouth, then closed it. A few seconds later, he nodded. “Okay …”

He didn’t sound very disappointed, and Sans could make out a tiny smile curling up his mouth. Papyrus had always liked sleepovers, and if Daddy was sleeping in their bed, that meant they would all be piling on it together.

They had had their room for as long as they could remember, but they had only actually been using it to sleep for a year or so, and they still climbed into Daddy’s bed about half the time if they couldn’t fall asleep by themselves. Their bed wasn’t as big as Daddy’s, but it would still fit him, and Sans was apparently really still once he fell asleep. Papyrus … well, he kicked a lot, but as long as they put him on the side of the bed close to the wall he wouldn’t fall off.

And their floor was clean. Papyrus made sure of that every night before they went to bed, picking up every single toy and sorting it away into its “proper place.”

Even though Sans’s arms felt like they were about to fall off, it only took a minute to drag Daddy the rest of the way across the floor. Getting him off the floor and onto the bed was almost as tough as the stairs, but they managed it, and once they got his top half on the mattress, Papyrus climbed up onto the bed, and pulled each of his legs up as Sans pushed them his way.

Daddy was still in his work clothes, but it would be way too hard to get him in his pajamas when he couldn’t even stand up. He had slept in his clothes before, so Sans just took off his shoes while Papyrus took off his tie, and they dropped them off the foot of the bed, ready to be collected in the morning.

Papyrus settled on Daddy’s right side, closer to the wall, while Sans laid down on his left, reaching across the nightstand to turn off the light. In the dark, he could better see the glow-in-the-dark paint Daddy had put on the ceiling, in the pattern of the constellations he had been reading about a lot lately. It had been there almost six months now, but it still made him smile just a little easier. He tugged the blankets over himself, and with Papyrus’s help, they got them over Daddy as well. Then Sans let his head rest on the pillow, and he shifted down into the mattress, biting back a groan at the soreness in his bones. Maybe Daddy could heal that in the morning.

Neither of them said anything for a few minutes, and for a while, Sans thought maybe Papyrus had already gone to sleep. But finally, Sans heard him shift around, not enough to move Daddy, but enough for Sans to hear the rustle of the sheets and the creak of the old mattress under them.

“Do you think he’ll always work this much?” Papyrus asked, lifting his head to look at Sans over Daddy’s chest.

Sans tilted his head to stare at Daddy’s arm, trying his best not to meet Papyrus’s eyes.

“I dunno.”

Papyrus leaned closer, just enough to be in view of Sans’s good eye. “He used to spend more time with us, didn’t he?”

“Yeah …” Sans murmured. He pulled the blankets over him more, focusing on Daddy’s breathing. “Ever since he started designing that Core thing, he’s always busy.”

Papyrus went quiet for a minute.

“Do you think it’s really important?” he asked at last, a little softer than before. “The Core?”

Sans just shrugged, still refusing to look up. “Seems like it.”

Papyrus didn’t say anything, and Sans thought that he had finally given up. Normally Sans would have been okay with answering questions. But tonight, he was tired, and Daddy was finally home, and it was the only time they really got to spend together, even if Daddy was already asleep and they would be asleep soon, too. When he woke up tomorrow morning, Daddy would probably already be getting ready for work, dropping them off at school before he ran off to the lab for another long day.

“When you get big, will you work all the time, too?”

Sans’s head snapped up so fast he almost hit Daddy with his skull. But Papyrus had ducked his head down, almost entirely hidden from Sans’s view.

“Huh?” Sans asked.

Papyrus grabbed onto the edge of Daddy’s shirt, squeezing it in his long fingers. “You’re smart like Daddy. Does that mean you’re gonna do a bunch of important work and not spend time with me no more?”

Sans started to reach over to grab his hand, but stopped, pulling it back at the last second. His chest hurt.

“You’re smart, too, Pap.”

“Are you gonna do that?” Papyrus asked again, looking up, as if he hadn’t heard Sans speak.

Sans’s smile tightened so much it hurt. He never understood how his mouth could hurt if it couldn’t open, but it did. Everything hurt, and every second he looked at his brother, it hurt more.

He looked away.

“No. I’ll always spend time with you,” he said, as loud as he dared, even though he probably could have played the drums right next to the bed without waking up Daddy at this point. After a few seconds, he looked back up, meeting Papyrus’s eyes again. “And so will Daddy. You’ll see. He’ll … he’ll finish this soon, and then he’ll be here with us like he used to. You’ll see. He will.”

Papyrus looked at him. Just looked at him, and Sans wasn’t sure whether his chest felt lighter or heavier the longer they stared at each other across Daddy’s chest.

At last, Papyrus reached over Daddy to take Sans’s hand. Sans didn’t resist, and let himself enjoy his brother’s fingers squeezing his own.

“I love you, Sans.”

Sans squeezed Papyrus’s fingers even harder. “Love you, too, Paps.”

He could see just enough of his brother to make out the smile on his face.

Then he closed his eyes, cuddling closer to Daddy’s side, and fell asleep to the warm thrum of two souls nearby.


	20. Chapter 16

**Notes for the Chapter:**

> So, ready for some more angst? No? Oh, uh ... give it a few chapters? Then it'll ... no, then it'll just get worse ... Whoops. Sorry. XD
> 
> I know many of the readers of this story have also read _Butterscotch and Bones_ , but if you haven't, that's my normal kind of writing: angst that turns into fluff. Not the other way around. I swear I'm not evil all the time.

His dad told him it would hurt.

Papyrus knew that. He knew Sans might not be as strong as him, but he definitely wasn’t weak. If Sans couldn’t take whatever their dad was doing, then it wasn’t going to be any fun. Papyrus knew that. Papyrus was totally ready to accept any pain that he had to.

It didn’t make it hurt any less.

His dad was very careful at first. During the first experiment, he asked Papyrus five times if it was too uncomfortable, if he needed a break, a glass of water, even a pillow under his neck. And every time, Papyrus said he was fine. He could handle it. It stung a little when his dad did what he called “healing efficiency tests,” hitting him with bone attacks to see how fast he would heal on his own, but it wasn’t all that bad.

If that had been the worst of it, maybe it _wouldn’t_ have been that bad.

But apparently, there had been something in particular his dad had been working on with Sans. The thing that had been bad enough to make him finally want to stop. Some sort of … injection. When he asked, his dad told him that it was the same stuff he and Sans had been grown in. Papyrus didn’t think it could be a bad thing, if it was what had made he and his brother exist in the first place. If it had made them grow before, it would be good for them now, wouldn’t it?

He had thought that the worst pain he would ever feel was when he cracked his leg when he was little.

He was wrong.

He didn’t scream. He wanted to. He wanted to scream so loud the building would fall down. But he didn’t. He had told his dad he would do this, he would get through it, he would help him finish his research, he would help him break the barrier and he would have done something important, he would have helped everyone be free and his brother would get to see the stars and everyone would be happy and—

He didn’t scream.

And he had thought his dad would be proud of him.

But when the experiment finished, his dad wasn’t looking at him. He didn’t offer him a pillow or a glass of water or even heal him. He was far too focused on writing things down in his notepad.

Papyrus waited. But his dad never looked at him. So after half an hour, when he finally felt like he could walk without falling over, he slipped out of the lab and went back home.

It got worse after that.

Almost every experiment started with an injection. Sometimes it was just an injection, writing down measurements from all the machines he was hooked up to, seeing how the stuff affected him. Other times, his dad waited until he had recovered a bit, then started another experiment, saying that he wanted to see how the injections had changed Papyrus’s ability to heal.

Sometimes it was more bone attacks. Sometimes it was electric shocks. Once, his dad called out his soul and poked at it, and Papyrus gritted his teeth so hard he swore he felt them crack.

He didn’t scream, though.

He wouldn’t scream.

Even if his dad didn’t ask him if he needed anything any more. Even if his dad barely talked to him the whole time he was there, just giving instructions and writing things down and muttering about how almost all the nutrient fluid had been used up and he needed to get better results soon. Even if he never told Papyrus he was doing a good job, or that he was proud of him.

Even if Papyrus could barely recognize the man in the white lab coat who used to be his dad.

Today, his dad had gone back to bone attacks. Apparently enough time had passed since he started getting those injections that his dad wanted to see whether the results had changed. It hurt less than it had the first time, or the second, or the third. Papyrus felt his HP drop, and he felt the pain, sort of. But it was distant. Dull.

Maybe it hurt just as much. Maybe he was just too focused on watching his dad’s face, and trying to see whether he noticed Papyrus hurting at all.

He didn’t heal Papyrus when he was finished. He had healed him the first time, after some time had passed, but now, he was too focused on writing down everything he had been muttering since the experiment began. Papyrus pushed himself up off the table, but his dad didn’t even turn around to face him. He waited. He watched. Still nothing. Just more pen strokes across the paper.

Papyrus stood there for a few minutes, just staring at his dad. Finally, after what must have been five whole minutes, his dad looked over his shoulder. Was it true, that you could feel someone staring at you even if you weren’t looking?

His dad looked irritated. Not much. But more than Papyrus was used to.

He thought there might have been a bit of concern there, too, but it was gone before he could be sure.

“Is something wrong?” his dad asked.

Papyrus’s hands shot up in front of him, his head shaking so fast he made himself dizzy.

“Oh, no, no, I’m alright! I’m just … a little …”

He trailed off, his shoulders slumping even as his hands curled close to his body to wring together. But his dad had already turned away, staring down at the notes in front of him and making new marks with an old ballpoint pen.

“Mm, good. Let me know if there are any lasting effects, anything that occurs over the next twenty-four hours is likely to be a result of the experiment and we’ll need to mark it in our notes.”

“Okay.”

His dad didn’t say anything else, writing so fast—and so illegibly—that Papyrus wondered how he would be able to read any of it later. Papyrus waited, fidgeting, ignoring the ache in his chest, the way his head spun and his legs wobbled as if they wouldn’t hold him up much longer.

His mouth set in a tight line.

No. He was strong. His dad had told him he could do this because he was strong.

He would be strong. He _had_ to be strong. For his dad.

For Sans.

He waited, for what felt like a long time, but his dad didn’t look up or say anything else. He just went on writing, just as fast, just as illegible. Papyrus glanced at the clock, shifted his weight, and cleared his throat.

“Um … Dad?”

“Mm?” his dad hummed, without turning around.

Papyrus waited a few seconds longer. Still, his dad said nothing.

“I’m going home.”

His dad’s hand paused, just long enough to give Papyrus hope. Then he went back to writing, waving his free hand. “Yes, fine, fine.”

Papyrus waited again. His dad kept writing.

“Are you … coming with me?” Papyrus asked, his mouth twitching into the tiniest hint of a hopeful smile. “To have dinner with Sans?”

His dad grunted. “No, not tonight, I really must get all these notes down before I forget anything.”

Papyrus had expected it—or he thought he had—but his shoulders still fell, and his smile still slipped away before he could stop it.

“Oh. Okay,” he murmured. He forced another smile, not as wide as the first, but good enough so that _maybe_ it would have fooled someone from a distance. If anyone had been looking at him in the first place. “I’ll see you later.”

His dad didn’t say anything. Papyrus stood there for another minute, then turned around and walked out of the lab with steps as slow and even and careful as he could manage. He wobbled once, but held himself up on the wall and kept on moving.

He could handle it. He told his dad he could handle it, and he could. It wasn’t so bad. He would be alright.

He would definitely, absolutely, without a doubt, be totally fine.

The walk home took longer than usual. It wasn’t actually very far from the lab to his house, but it had seemed a lot shorter when he was with his dad and his brother, or at least _one_ of them. Or … anyone, really. Apparently it was late enough that most of the other monsters had already gone home, and Papyrus came across almost no one else as he made his way through Hotland. Normally he would have bounded around the conveyor belts when he reached them, trying out new tricks and taking advantage of the added momentum to move even faster, but now he found himself just standing still, letting the belts carry him forward on their own.

He didn’t want to come back this same way tomorrow. He didn’t want to go back there ever again.

But … he had to, didn’t he? He had said he would. And he had to do what he had said he was going to do.

The lights were already on when the house came into view. He wasn’t sure whether to be glad or disappointed—he wanted to see Sans, he _always_ wanted to see Sans, but sometimes it was easier if he could be by himself for a while, look in the mirror and remind himself over and over again that he was okay, until it got easier to believe.

Well. He wasn’t about to let himself be thwarted by the absence of a mirror, was he?

He paused ten yards from the house, squaring his shoulders and holding his head up high. He took a deep breath and let it out slowly. He was still Papyrus. He was okay. He was helping his dad, doing something good, doing something _important,_ just like he had always wanted to do. Even if it was … uncomfortable … and even if his dad was acting funny, that wouldn’t stop him from being proud.

And soon, everyone else would be proud of him, too.

Papyrus smiled, a little more easily now, and strode to the front door.

But the second he opened it, his confident smile began to fall.

Yes. It would have been much easier if Sans hadn’t been home.

Or, at least, if he hadn’t been standing in the middle of the living room, staring at the door with wide, startled sockets, his whole form tense, as if he had been standing there, maybe walking back and forth across the room, for a long while.

Now, he was still. Completely still, the lights in his eyes almost gone as he looked his brother over from head to toe.

“Papyrus?” he breathed, a tiny crease in his browbone as his shock began to fade.

Papyrus took a deep breath, stood up straight, and gave Sans his best smile.

“Oh! Hello, Sans!” he said, as if he hadn’t been staring at him for more than fifteen seconds now. “How was your day?”

But Sans didn’t even seem to hear him. He snapped out of his reverie and crossed the room to stand a few feet in front of him, his browbone furrowed and his head tilted in concern. “Bro, what happened? You’re all …”

Papyrus paused, then looked down at himself. Oh. He hadn’t realized that today’s experiment would leave marks. It hadn’t hurt as bad as some of the others, so he had just assumed that the only lasting effects would be his usual tiredness, and the ache in his chest. But there were faint marks on his arms, little chips and scrapes. The same on his lower legs. Now that he paid attention to it, he thought he could feel a few on his skull.

He looked back to Sans, and nearly winced at the widening of his eyelights, the tightening of his smile. The curling of his fists. The silent threat toward anyone who had hurt him, anyone who had _dared_ to cross his brother.

Sans wasn’t bad. He wasn’t mean or violent.

But Papyrus had never forgotten the way those kids who had teased him had run and screamed when Sans caught them backing him into a corner and laughing until he cried.

“I’m fine, don’t worry!” he said, before he had time to think. Dad had told him to say things like that, and he had agreed, but so far he had just avoided it, he had never looked his brother in the eyes and _told him something that wasn’t true._ But his mouth was still open, and his voice was still coming out. “I just … tripped. On the way home.”

His soul twisted. He didn’t want to lie to Sans. He didn’t want to lie _at all._

He hated lying. Lying never did anything good. And this was lying to _his brother,_ who meant more to him than anyone else in the world.

Lying when he had just told Sans how bad lying was.

Sans’s browbone furrowed, and he took a few steps forward, staring at Papyrus as if the answers might fall out of his skull if he looked hard enough.

“Where were you, anyway?” he asked. “You said this morning you were going out, but you didn’t say where.”

Papyrus wrung his hands, looking away.

“Oh, well … you know. Ever since I finished school I’ve just been at home all the time, and I thought it would be a good idea to go out and do things! Exciting things. Interesting things. Fun things. With other people!”

Sans looked at him. Just looked at him, so deeply Papyrus couldn’t help but glance around the room and shift some more. Was this how Sans had felt all those times Papyrus stared at him, accusing, _knowing_ that he had done something or gotten hurt or was sad or there was something he really should have been talking about but wasn’t? Had Papyrus really thought making Sans feel like _this_ was a good idea?

“You’re … making friends, then?” Sans asked at last, though he didn’t sound remotely convinced.

Still, Papyrus beamed, as genuinely as he could, nodding so fast his head spun. “Yes! Of course! I make friends wherever I go!”

Sans didn’t believe him. Papyrus knew, deep down, that he wouldn’t, no more than he would believe Sans if he was _so obviously lying,_ but that hadn’t stopped him from hoping. It hadn’t stopped him from wishing he wouldn’t have to see that pained, worried look on his brother’s face.

“Pap, please. Tell me what happened.”

But Papyrus kept smiling, even though it hurt, even though it went against everything he had thought was right. Everything he _still_ thought was right.

“I just tripped, Sans,” he forced out, and it was like he could feel his dad’s eyes watching him, repeating those words over and over in his head. “I’m fine!”

His smile trembled, but he held it in place, staring down at his brother as much as he wanted to look away. Sans looked back to him. Had Sans always looked at him like that? So intent? So searching? Had it always felt like he could see _everything_ Papyrus tried to hide?

Had Papyrus ever tried to hide before?

It felt like five minutes later that Sans’s shoulders sagged, though with more resignation than relief. His face tightened, but he managed a small nod.

“Okay,” he said, even though he didn’t sound very “okay” at all, and Papyrus had a feeling Sans was faking his smile just as much as he was. He nodded toward the table. “I ordered in for tonight. Since you weren’t home and I didn’t want to risk blowing up the kitchen trying to cook myself. You hungry?”

Papyrus wasn’t very hungry. He was tired, and he hurt, and food didn’t sound very nice at all right now. But Sans was looking at him with such hope in his eyes, and he had set the table perfectly, even putting the bagged food on plates, and as much as Sans cared about some things in his life he had never cared about simple housework. So Papyrus smiled and nodded.

They ate in silence. Papyrus spent more time pushing his food around with his utensils than actually eating. Sans noticed, he was sure, but he didn’t say anything. Or, at least, as soon as he was _about_ to say something, Papyrus took a particularly large bite of food and hummed in appreciation, and Sans stayed silent.

Papyrus tried to help with the dishes, but Sans insisted that he would get them, and Papyrus should head up to bed. Papyrus almost argued, but then Sans nudged him toward the stairs, and his legs moved without his permission, and he couldn’t quite stop them. Sans guided him up the stairs, and down the hall into his bedroom. Even after sleeping there alone for the past nine years, he sometimes had to remind himself that his door was the second, not the first. On his request, Sans had taken their early childhood bedroom, and Papyrus’s room had been renovated from the space that used to hold all his dad’s old boxes.

It was a good room. A _clean_ room, much cleaner than his dad’s, and even cleaner than Sans. It was his and he had decorated it all by himself and he loved it.

So why did he wish he could go sleep in Sans’s room instead?

He thought about saying something about it, but he didn’t. He changed into his pajamas and laid down in his bed, and a minute later Sans came in. Papyrus thought he was just there to wish him goodnight, but Sans didn’t say anything. He sat down on the edge of the bed and rolled back the blankets to show Papyrus’s torso.

“I’m just gonna heal you a little, okay?” he asked, meeting Papyrus’s eyes with a raised brow.

Papyrus started to protest, but everything that came to his mouth sounded wrong, and finally, he let out a soft breath and nodded. Sans smiled, and Papyrus thought he saw relief glowing in his eyes.

When Sans laid his hands on his chest and let his magic flow out, Papyrus pretended he didn’t see his dad’s face with every injury he healed.

Sans looked a little happier once his HP was back up, and Papyrus wasn’t going to take away anything that would make his brother’s smile a little more real.

For a second, as Sans slipped out of the room, Papyrus wanted to ask him to stay. But as soon as his mouth opened, the words caught in his throat, and he forced them back down enough to smile when Sans glanced over his shoulder and murmured a final goodnight.

His footsteps faded before disappearing down the hall.

Papyrus wondered if his room had always looked this scary in the dark.

He pulled up the covers. He shifted back and forth on the mattress. He fluffed his pillow, three times, turned on both his sides, his front, and his back once again, but his sockets wouldn’t close. He stared at the ceiling, and counted all the little cracks he had never noticed and tried to figure out when they had appeared.

His mouth pressed together so tightly he thought his teeth might crack, too.

He didn’t want to lie. He hated lying. He didn’t want to lie to Sans, he didn’t want to lie to _anyone._

But …

If Sans knew, he would feel bad that Papyrus was hurting instead of him. If Sans knew … he would probably try to make them stop. He had never let Papyrus get hurt, in however small a way, if there was anything he could do about it. It wouldn’t matter to him how much they would gain if they kept going. He would make their dad stop. He would make Papyrus stop.

So Sans couldn’t know.

It would hurt for a while, yes. It would be … uncomfortable, and a little scary. And his dad would probably keep acting funny. And Papyrus would keep having to lie to his brother.

But Sans would be safe. He might be confused and worried, but he wouldn’t be hurting so bad. And … it would be worth it. It would work, and it would be more than worth it. They would get to see the surface. He would get to ride around in a real car, soaring down a real street, feel the sun he had heard so much about in his storybooks when he was a babybones.

And Sans could see the stars. The real stars.

That would be more than worth all of this, wouldn’t it?

Sans would be happy. And maybe he wouldn’t be quite so upset that Papyrus had lied to him to make it happen.

Everyone would be happy. Everyone in the whole Underground. Sans and his dad and Dr. Japer and old Mrs. Drenton and Dr. Lemming and Dr. Frewth and everyone Papyrus had ever met. And it would be him who helped make them happy.

Yes. That was worth all of this and so much more.

Papyrus closed his eyes and tried to smile, but the smile wouldn’t come. His chest hurt, and his head felt funny, and he wasn’t sure whether he wanted to run laps around all of Hotland or never move again. It was a funny feeling. It wasn’t a good feeling. He tried to ignore it, but it wouldn’t go away.

And all he could think about was his dad, turned away from him, focused on his papers while Papyrus limped out of the room.

It took more than two hours before he finally fell asleep.


	21. Chapter 17

**Notes for the Chapter:**

> Bit of a break from the angst here ... well, sort of. Kind of. A little. More B.S. science!

There was something wrong with Papyrus.

There was something very, _very_ wrong with Papyrus, and Sans had no idea what it was, and it was about to make his skull explode.

Papyrus had always been more than people thought he was, at least from their first impression. He acted like a kid, and people took that trait and labeled him and left it at that. They usually didn’t take time to really listen to him, to get to know him beyond his surface traits. He acted like a kid, but Papyrus was far wiser than anyone gave him credit for.

But he wasn’t very good at hiding when something was wrong.

And usually, he didn’t try.

But now …

Something was wrong. Something was wrong, and Papyrus wasn’t telling him what it was, and no matter what the problem was, the fact that he hadn’t _said_ anything about it was enough to make Sans lose sleep. Was he mad that Sans had been hiding stuff from him before? Was he hiding this to spite him? No, Papyrus wasn’t spiteful, if he was upset he would say something about it. Was someone threatening him? Who would threaten _Papyrus?_ Everyone loved him. Even those that didn’t respect him still wouldn’t dare hurt him.

But he was hurting. Something was hurting him, and he wouldn’t tell Sans what it was.

And their dad …

… Sans still remembered those days when they were younger and their dad had become so engrossed in his work that he had gotten just a bit neglectful. Never anything serious—aside from the time he forgot to go grocery shopping for two weeks and only realized after four days that Sans and Papyrus had been getting all their food from Mrs. Drenton. But while he was in the midst of an important project, he would spend less and less time with them, rushing through meals or skipping out on regular family activities so he could get back to work. When he had been working on the Core, it had occasionally gotten so serious that Dr. Japer had dragged him home and locked him out of the lab until he spent a few days resting and spending time with his sons.

Things had changed after he finished the Core. He still went to work, of course, and he still had little projects that held his attention from time to time. But he spent far more time at home, far more time with his sons. If he had a choice between work and spending time with them, he would always choose the latter.

Sans hadn’t really thought about it then. He had gotten used to his dad not being with them much, and he had already started college by that point. He was too focused on his classes to really notice the difference.

But Papyrus had gone on and on about it. Every day after school, for as long as Sans could remember, he would stay in the living room, waiting for their dad to get home so he could be the first person to greet him. Sans had done that, too, once. But he had given up. Papyrus hadn’t. And when their dad finally lightened up on his workload, Papyrus might as well have been given a key to the barrier for the size of the smile on his face.

Sans didn’t really know how much time Papyrus and his dad had been spending together before he started working at the lab. Maybe it was a lot. Or maybe it was just a little, just enough to make a difference from those old days when his work had taken up so much of his life.

Maybe it was enough so that Papyrus felt the change now that his dad was engrossed in work once more.

Sans didn’t know _what_ had him so engrossed. Maybe he had taken to studying the human’s records, now that the experiments with Sans were done? Maybe he had started researching the barrier again? He had been passionate about that, really passionate, and even if he had agreed to stop the tests with Sans, that didn’t mean he would stop focusing on the barrier completely.

That might have been exciting, a few weeks ago. No, it _would_ have been exciting. That was what he had wanted, wasn’t it? For his dad to be passionate about something again. For him to try, for him to _care._ But now …

He wasn’t even home for dinner a lot of the time, and he was gone in the mornings before Sans even woke up. Sometimes two days went by without him and Sans talking at all. Sans had stopped coming by the main lab for supplies, he had everything he needed in his own lab. On the rare occasions they _did_ see each other, his dad seemed … distracted. Like he couldn’t stand to be away from his work for however brief a time. Was he spending any more time with Papyrus? Was he this distant with Papyrus? If he was gone at the lab all day …

Maybe that was it. Papyrus tended to worry about people a lot, even if his way of expressing it was completely his own. And he had always worried more over Sans and their dad, maybe because both of them tended to neglect themselves when in the middle of work, or maybe just because they were family.

Either way, their dad definitely hadn’t been acting normally lately, and that fact was probably on Papyrus’s mind even more than it was on Sans’s.

If that was the case, then why hadn’t Papyrus just _said_ something?

Why had he been late coming home twice over the past two weeks, when he had _always_ insisted on getting home early enough to make dinner for everyone?

And why wouldn’t he tell him how he had gotten hurt?

Something was going on. Something was definitely going on. Sans just had no idea what it was.

But if someone was hurting his brother, if someone was making it so he didn’t feel comfortable telling Sans …

He would figure it out. One way or another, he would find out what was going on, and he would fix it.

But as hard as it was to get thoughts of his brother out of his head, he had far too many things to focus on now to spend time worrying about something he couldn’t fix right away.

Namely, making adjustments to the T.F. machine, now tucked away in his own private lab.

His dad had been right. It _was_ much easier to get accurate readings when he didn’t have interference, and it was a lot easier to focus on his work when he didn’t have the clutter of the rest of the lab around him. Not that he didn’t appreciate clutter—his room was a good example of that on any given day. But there was something about a nice, clean lab that made measuring the spacetime continuum seem that much simpler.

Or maybe it was just the lack of dust in the air.

He didn’t notice the footsteps outside the door until it opened, and he was smiling before he even turned around to look at Alphys as she slipped inside. She still knocked half the time, even though he had told her she didn’t have to, and he knew it was going to be a long time before she felt as much at home in this lab as he did.

He really needed to talk to his dad about getting her a lab she could use for her own stuff.

But for now, his eyes fell on the bag hanging at Alphys’s side, and a single glance at the expression on her face was enough to make his own smile stretch all the way across his cheekbones.

“You finished the program?”

Alphys reached into her bag and pulled out her laptop, holding it up with a shy smile.

“J-just got the l-last bit done last night.”

Sans’s smile somehow grew even wider, and he only barely held himself back from wrapping her in a tight hug.

“Alphys, you’re amazing,” he said, shaking his head in marvel. “Remind me, I owe you some good anime DVDs for this.”

Alphys chuckled nervously and ducked her head, though not fast enough to hide the eager gleam in her eyes. “It’s n-nothing, Sans, I’m involved in this r-research, too.”

Sans waved his hand in dismissal.

“Still, I could never do this on my own. You know I suck at writing code.”

Alphys’s face flushed. She cleared her throat and scurried around him toward the machine. She sat down beside it, took out a cord, plugging one end into her laptop and the other into the port in the machine.

“O-okay, let’s s-see if it works …”

Sans knelt at her side as she opened her laptop and started up the program. It took a minute for the computer to connect to the machine properly—Alphys’s laptop seemed to be a good deal newer than the technology used to build the machine—but finally the program began to run, streams of numbers flying across the screen.

“So what’s it doing?” Sans asked at last. “You never told me exactly what you were planning.”

Alphys didn’t look at him, her attention still intently focused on her laptop. Sometimes she really reminded him of his dad in the middle of a particularly engaging project.

“W-well … the original intent of the machine was to measure the spacetime c-continuum in _t-this_ timeline, right?” she asked, talking to herself as much as to him, her browbone furrowed in concentration. “B-but … if there are _o-other_ timelines … then the machine would s-still pick up some of their readings. It j-just isn’t d-designed to focus on it, a-and without all the i-information it’s d-difficult to c-confirm anything.”

She typed, inputting instructions too fast for Sans to make out before they disappeared and the program started on something else.

“So t-this software m-modifies the machine’s original programming, and t-tells it to lock on t-to the outlying r-readings and then r-remove what we h-hypothesize should be the clean readings from o-our timeline. That s-should give us only the d-data we want to s-study.”

He chuckled again, a breathy, wondrous sound, as he peered closer to the screen.

“Again, you’re amazing. You did this in a _week_? ”

“E-eight days,” she muttered, tilting her head further away, though that did little to hide the deep red flush now covering her entire face.

His mouth curled up further, his eyes softer as he thought of every amazing thing she had built over the years, from the little inventions made of stuff her parents had thrown out to the programs she had submitted “anonymously” to help the development of the Core.

“You know, that offer to put in an application doesn’t expire.”

Alphys jerked her head around to face him, eyes wide, just staring for a moment before she shook her head, so fast her glasses almost flew off her face. Sans put his hands up in mock surrender.

“I know, I know,” he replied, laughing, though there wasn’t much humor to it. “Just gotta tell you every now and then. You could do so much good in a real lab.”

He must have said the same thing at least fifteen times in the past year, since the first time he had interned at the lab and talked about getting a long-term job there, and her reaction had always been the same. He didn’t know why he kept trying. But it was hard to look at someone like Alphys, and everything she could do, and not take every chance to tell her.

“J-just s-start the m-machine,” she murmured, tucking her hands into her lap and staring down at the laptop screen.

Sans sighed, a little more dramatically than necessary, then walked around her and pushed a few buttons on the control panel to set the machine running. It hummed and jittered, then buzzed, and seconds later, the buttons lit up and the program on Alphys’s screen burst into life.

For a few minutes, both of them just watched. At first, the program and the machine seemed to be syncing up, the program making sense of the input it was given and putting it into a format they could actually understand. Neither of them spoke, though Alphys jittered so hard she nearly vibrated and Sans shifted his weight from foot to foot with each second that passed, resisting the urge to gnaw at his fingertips like he used to do when he was a kid.

Then a new window popped up on the screen, mostly black with lines of various colors waving and shifting from side to side.

Sans froze.

Alphys leaned in closer, her jittering apparently forgotten as her jaw dropped and she pushed her glasses up on her nose.

“Whoa,” she murmured.

Sans huffed a humorless laugh, his sockets as wide as they had been in weeks. “You got that right.”

Alphys bit her lip and adjusted the laptop on her legs.

“I-I mean, it’s not p-precise, but given the predicted d-distance and how t-that would skew the numbers …”

“Uh-huh.”

Sans stared at the center line, more defined than the others—though it was hard to read the numbers with them moving around, it didn’t take more than a glance to see they fit perfectly within Dr. Billington’s projected range. The others waved along on either side of it, more detailed the closer they got to the center, blurring as they spread further apart.

It wasn’t an entirely _accurate_ representation, he knew. Parallel universes didn’t lay on top of one another like pieces of bread on a sandwich. But Alphys had always had a gift for putting complicated data into something easy to visualize, and Sans knew even his dumbest classmates in his first years of college could have understood what those lines meant.

“S-so it’s t-true,” Alphys said at last, even though she didn’t have to.

Sans let out a long breath, shaking his head as he peered closer to the screen. “Yeah.”

Silence again. Alphys fidgeted, and Sans couldn’t quite tell whether it was nervous or happy.

“We … I … it’s n-not like I didn’t think we were _r-right,_ Sans, it’s j-just—”

“I know, Alphys,” he cut her off, resting a hand on her shoulder and giving it a brief squeeze. He could feel her shaking under him. “It’s … different when you can see it for yourself.”

Alphys nodded, once, then several more times. “B-but this is unmistakable. T-there … there might be other explanations, b-but I d-don’t think … this is … S-Sans, this is r-revolutionary! You d-discovered parallel u-universes!”

“ _We_ discovered parallel universes,” he replied, without missing a beat. He stared at her, even as she refused to meet his gaze. “Don’t you dare try to give me all the credit. If we publish a paper, your name’s going on it, too. _Before_ mine. Your idea and your program. End of discussion. ”

Alphys’s whole face went red, but she couldn’t hide the hint of a smile that curled up her lips. Sans just grinned and looked back to the screen.

They had done it. They had really done it. Everything Dr. Billington had started … they had made the next big leap.

This would be huge. It would be … probably one of the highlights of his career, a career that had hardly even gotten started. The knowledge alone would have been worth a decade of work, but the applications …

The applications.

Everything he had ever studied on parallel universes had just been theory. But … it had been educated theory. Logical theory. And now that he had solid evidence they were real, now that wasn’t just some idea a scientist thought up when they didn’t have anything else to do …

How many were there? Had there always been that many, or had they branched off over time? What had caused them?

What was _in_ them?

Parallel universe theory suggested that there were infinite universes, and that even the tiniest change at one point rippled out into an entirely different future. If that was the case, then there should be one for every possible variant of every decision that was ever made in the history of … everything. More than he would ever be able to view or study. More than _anyone_ would have time to study.

But …

There were clearly at least a few that were close by—whatever “close by” meant in terms of parallel universes. Maybe they were only slightly different from this one, but if there were bigger changes … if there was a universe where all this research done into breaking the barrier, one way or another, had actually been _successful …_

… what if he could view it? What if he could find a way to get enough information about what had happened in that universe to see how they had broken the barrier? And if it was doable, what if he could replicate it?

He could find out how they had done it, and do it here, without all the trials and errors. He would know _exactly_ what he needed to do, and even if it wasn’t easy, at least he would know that it _could_ work.

He could get them all out of here.

Surely, there was a universe where they already _were_ out of here. If he could just find it, if he could _study_ it …

Everything his dad had hoped for them …

They could do it. No one would have to get hurt. It would be a while, it would probably be a _long_ while, but he could do it. With Alphys at his side, they could find a way to look into those other universes, find the right one, and get everyone out of this hole in the ground.

He turned to Alphys and flashed her another wide again. Alphys blushed deeper, but couldn’t quite hide her smile in return.

Yes. They were going to get out of here.

All they needed was time.


	22. Chapter 18

**Notes for the Chapter:**

> Who's ready to rejoin our dysfunctional family? ;)

Two weeks.

Two weeks, and he had already learned more than in the four he had worked with Sans.

Granted, he had been more hesitant then. He had been too focused on the consequences, on the fact that he was doing the experiments _at all,_ to think about what would really give the most useful information, and it had only been in the last week that he had really reached a breakthrough. Now, he knew exactly what he was doing. He knew what was important and what wasn’t.

And, of course, Papyrus didn’t need nearly as much time to recover between experiments as Sans had.

He didn’t complain. Gaster could see him in pain sometimes, but … it was brief. And he handled it well. He had known what he was getting into, he had _offered,_ and they were getting so much more done and soon it would all be worth it. Papyrus _knew_ that. He knew what they were working for.

Soon, he would get to see it.

Gaster filled in the holes left in his research with Sans with ease. He wasn’t going to waste precious time trying things out that _might_ work. He knew what to focus on. He knew where his energy—and Papyrus’s—was best spent. And he dove headfirst into every experiment he had never gotten the chance to work on before.

He just hadn’t realized how little he had thought about what he would do once all those experiments were completed.

Fragments of Papyrus’s soul survived just as long when separated from his body as Sans’s—though that time increased significantly with the nutrient fluid injections. A maximum of twenty minutes before turning to dust. He had studied the soul fragments from every angle possible, learned everything he could from them. They certainly survived far longer than most monster souls, and even a good deal longer than boss monster souls.

But twenty minutes wasn’t going to be enough. And he still didn’t know if the souls would survive once their associated body was completely destroyed.

After only two weeks, the entire jar of nutrient fluid, the jar he had thought would never run out, had gone empty.

And Gaster was left at a dead end.

Sans and Papyrus were different from most monsters, certainly. Their vital readings and test results consistently fell somewhere in between a monster’s and a human’s, and their souls were a good deal more resilient than most monsters’. That was a start. But it wasn’t enough to start work on synthetic souls.

He spent several hours digging around the lab after that, sending Papyrus home to rest while he figured out what he was going to do next. He poured through the human’s file, searching for anything he hadn’t studied, anything he hadn’t considered, anything he could _do,_ he had said he would do this, he had promised himself he would do this, he had given up before and he _wasn’t_ going to give up again.

That was when he found the S.E.

It had been stuffed in the back of the closet, even further back than the remaining nutrient fluid. Just a small vial filled with fluid as thick and red as human blood. The last time he had even thought about it was when he made that last batch of nutrient fluid, months before the boys were born. He had brushed it off as useless aside from that. He had been so excited when he first got it, so determined that it would lead to a breakthrough. And it had done nothing. He had spent months designing the extractor, weeks extracting small amounts from each of the human souls to ensure he never took too much, months more testing it in every way he could think of, and all it had given him was a bunch of leftover nutrient fluid.

And two sons.

He paused and kicked himself for forgetting, even for a second, how grateful he was for that fact.

But it wasn’t like he was going to make any more children. So what use was the S.E. to him now?

He could make more nutrient fluid, of course. It would take time, but he still had the recipe, and magic-concentrated food wasn’t all that hard to come by. He didn’t need much to make a full batch of nutrient fluid.

But …

That was what he had been doing this whole time. It had helped things, certainly, but it wasn’t enough. Papyrus’s readings were different, closer to human’s, but they weren’t close _enough._

But up until this point, he had only been using the diluted solution. Nutrient fluid made with a small amount of S.E. Clearly enough to make a difference, but not particularly strong. He had never considered using it straight before, and the thought of _giving_ it to monsters at all, especially undiluted, had never crossed his mind, but now …

… after what he had already seen the S.E. _do_ …

“Yes, I think so,” he murmured, nodding to himself as he stared down at the papers on his desk.

“What do you think?”

Gaster blinked, then turned to face Papyrus, standing just a few yards behind him. Right. He had forgotten that Papyrus still came in in the mornings. He hadn’t asked him to come in, he had told him he was free to wait at home until he figured out what they were going to do next, but Papyrus insisted that he could help in _some_ way, even if it was just offering encouragement or keeping the lab tidy.

Even if Gaster hardly talked to him all day.

It took a few seconds before his mind processed the question. As the words clicked, Gaster looked away, staring down at his own notes as he let his jumbled thoughts settle into a proper sentence.

“I’ve been thinking of a new experiment,” he started, looking back over his shoulder to face Papyrus. “Something … different from what we’ve done before.”

Something flashed across Papyrus’s face too fast for Gaster to see. He managed a smile, shaky and small, and tilted his head in that childlike curiosity that had never really gone away.

Gaster’s chest hurt.

Then he looked away.

It would be worth it. He had to believe that. And Papyrus had agreed to this. He had _eagerly_ agreed to this, and he wouldn’t have come back to the lab if he didn’t want to help, right?

They weren’t going to get anything done if he kept hesitating.

He looked back.

“I believe we may be able to achieve better results using … concentrated S.E.”

Papyrus stared at him, the cogs in his head almost audibly turning. “S.E.? That … stuff you said came from humans?”

“Yes,” Gaster replied. “You were grown in it. You and your brother. A solution of S.E. and concentrated nutrients.”

Papyrus looked down at himself, as if he could somehow see the composition of his bones just by staring at them. He turned to Gaster again.

“Is that why we’re … unique?”

Gaster hummed, turning his gaze to the wall.

“I believe so,” he murmured, as much to himself as to Papyrus. “Thus far, we’ve only been using a diluted solution. I think that injecting concentrated S.E. will … bring about more notable changes.”

He didn’t need to turn to hear Papyrus fidgeting again. It was a strange sound. Papyrus certainly fidgeted sometimes, but only if he was particularly anxious about something. Gaster held back the urge to ask him to stay still.

It took nearly a minute for his voice to lift up again, hesitant, as unsure as the shifting of his feet.

“You want to … change me?”

Gaster blinked, browbone furrowed. He hadn’t thought of it like that. It hadn’t crossed his mind, even when he first thought of giving Sans nutrient fluid injections. He had wanted to see how much of a difference nutrient fluid could make at this point, now that the boys were grown, it had made a difference that they were _gestated_ in it, but he had to see whether it would make a difference now. And it had. Maybe it hadn’t been enough, but it _had_ made a difference.

It made Papyrus’s readings more like a human’s.

Was that changing him?

“I … want to make you stronger,” he said, very slowly, even though the words felt wrong in his head.

He looked up enough to meet Papyrus’s eyes. Papyrus stared at him for a few seconds, his expression, for once, completely unreadable.

“Oh.” He shifted again, and Gaster had to grit his teeth to stop himself from asking him to _just stay still._ Papyrus looked from side to side, grinding his teeth. “And … if I’m strong … then that will help me help break the barrier?”

Gaster paused. Once again, he looked at Papyrus. Looked at his son. Who had stuck with him, even when things got difficult. Whose eyes shone with just as much determination as his own. Determination to see this through to the end.

His eyes shifted back to the vial of red liquid sitting on his desk.

There wasn’t much, now that he thought of it. There was hardly any, compared to the stock he remembered having all those years ago. Before Sans and Papyrus, he had used it almost liberally, testing it out on this and that even though he had no idea of how to use it to break the barrier. Back when he thought it might be useful, he had extracted as much from the souls as he could without risking changing their composition. If he too away too much of their essence, they might not be able to do their part to break the barrier, and then they would be even worse off than they already were.

He couldn’t take any more from the souls. And his liberal experimentation had eaten up a good chunk of his stock. Almost all of the rest of it had been used to make more nutrient fluid to grow the boys in, even if he didn’t need much to make a full batch. Now, he had only that one large vial left. Perhaps enough for four doses, if he used as much as he was planning.

Four doses.

Was it really worth using up the last of the S.E. for an experiment he didn’t even know would do any good?

Would making Papyrus “strong” actually get them where they needed to be?

Even if he reached a breakthrough, he wouldn’t be able to replicate it. He wouldn’t be able to use it to grow an artificial soul, or to strengthen it. But … the amount of S.E. remaining wouldn’t have been able to do that anyway.

If he _did_ reach a breakthrough, if he was sure that he would able to use S.E. to create artificial souls … he could ask the king for more. Surely the king would understand. He had always trusted Gaster’s judgment—sometimes even if he really shouldn’t have. If Gaster had good reason to believe that extracting a bit more of the S.E. from the human souls would help, then surely the king would allow him to do so.

And he wouldn’t waste it this time. He would know exactly what to use it for, no more silly experiments with nutrient fluid.

Even if silly experiments with nutrient fluid was what had got him here in the first place.

If he could get this to work with Papyrus, if he could get his soul strong enough to mimic a human’s by absorbing enough of the S.E. …

Maybe they wouldn’t need to create two artificial souls.

Monsters could absorb human souls.

If Papyrus got strong enough, if his soul was strong enough to mimic a human’s … would that rule still apply?

Could he absorb the five human souls they currently had and count as one himself? That would leave only one. And he could work with that. Making one was much easier than making two. If he could just get close enough with these four doses, if he could get Papyrus to that point …

This could really work.

Everything he had hoped for … everything he had given up on, everything _everyone_ had given up on, everything that they had thought was either impossible or too far in the future to even imagine …

“Yes, Papyrus,” he said at last, holding his head higher, his shoulders straighter, looking at his son with eyes that he hoped looked half as hopeful as he felt. “If we can make you strong enough … I believe you can.”

*

He had originally planned to give the doses as quickly as possible, but after the initial tests, he decided to space them out by two days.

It was probably better this way. Papyrus’s body would have more time to fully absorb the S.E., and if he was going to be playing such an active role in this experiment, then he needed time to recover as fully as possible.

Gaster still took readings between each of the doses, seeing whether his vitals had changed, whether there were any notable differences in his healing speed or his soul. And there were. Not as much as he needed, not as much as a human, but significant. Enough to justify continuing. Enough to justify using up the rest of the S.E. to see this experiment through to the end.

That didn’t make him any less desperate for results when the day of the last dose came.

He needed another test. Something else to see how far Papyrus had come, whether this had all been a waste of time, whether it wouldn’t be quite good enough or whether it was something they could keep pursuing, even if there was no more S.E. to be found.

And it took him less than an hour to think of a way to start.

Papyrus sat down in the chair as soon as he arrived, just as he had every other day for more than a week. He knew the routine by now. S.E. and a bit of testing on one day, all testing on the other. Gaster tried to keep the tests fairly simple on the days of the injections, but Papyrus always insisted he was fine, he could take whatever Gaster needed to do, and it was getting harder and harder not to take him at his word. Especially when he could get results so much quicker.

Gaster stepped up beside his son, checking to make sure everything was in place before he turned to him again.

He pointed to the wall a good fifteen feet away, once covered with just as much junk as the others, but now cleared away, as empty as it had been decades ago when he had actually used it for its intended purpose.

“As soon as you feel … recovered enough from this dose, I want you to attack that wall.”

“Attack the wall?” Papyrus repeated, jerking his whole body around to face him so fast he almost fell out of the chair.

Gaster gave him an odd look, then nodded.

“Yes. We need to see if your attacks are strengthened by the injections. It’s impossible to compare your baseline attack strength to a human’s, given that human attacks aren’t magically-based, so we need to see if the concentrated S.E. really does improve attack strength as well as other measurements. I already have a good measurement of your regular attack strength, so all we need to do is see how well you perform after the injection.”

Papyrus looked at the wall Gaster had pointed to, his browbone furrowing before he looked to him again.

“But won’t the wall get hurt if I attack it?”

Gaster came very close to snapping at him before he clamped his mouth shut. He had forgotten about that little quirk of Papyrus’s. It had been so long since he had been a child, close to tears after he dropped one of his dolls for fear that he had hurt her when she hit the ground. He must know by now that things couldn’t feel pain. They couldn’t be hurt.

He took a deep breath and let it out slow.

“It’s reinforced, and very resilient. The building will be fine, I’ve thrown much worse at it. And we’re alone here, you’re not going to hurt anyone.”

But Papyrus’s face still twisted in uncertainty, his eyes drifting to the wall before they fell on Gaster again. He shifted his weight from foot to foot. “You never asked me to attack things before.”

Gaster bit back the irritated words that pressed against the backs of his teeth. Snapping wasn’t going to help. Snapping had _never_ helped, he had never been the _type_ to snap, but somehow it was getting harder and harder the more Papyrus delayed experiments with his ramblings. He took a deep breath.

“The experiments we’ve done so far haven’t been … we need to branch out. Try something new,” he said, though, judging by Papyrus’s face, he wasn’t making much sense. He let out his breath in a faint sigh. “The nutrient fluid I gave you before contained a significant amount of magical material as well as concentrated S.E. It made you different, but it balanced out the … human material with monster material, so to speak. I want to see if concentrated S.E. has made your attacks … not only stronger, but more … like a human’s.”

“But you said humans don’t have magical attacks,” Papyrus replied, head tilted to one side.

Gaster just looked at him and gave a small nod. “Yes.”

Neither of them spoke for a few seconds. Papyrus ground his teeth, fidgeting with his hands.

“So … what do you think will happen?”

“I don’t know. That’s why we’re testing this,” Gaster replied. Papyrus looked at him, expectant, as if he thought he might get a more expansive answer. An answer that Gaster racked his head for, but one he couldn’t find. He huffed and turned away, back to the little metal table with his supplies. “We need to start.”

He could feel Papyrus’s eyes on him, but neither of them said anything else.

He filled up the syringe with the last fourth of the S.E. remaining in the vial. It wasn’t very much, but it was concentrated, and even this much had made him nervous the first time he administered it. But he had to strike a balance somewhere, and if he spent too much time giving extremely small doses, he would never get anything done. Sans had handled the nutrient fluid, and Papyrus had handled three doses of pure S.E. fine, too.

The needle went in much easier than it had the first few times. Gaster had virtually mastered his technique, and Papyrus seemed to be used to the sensation of something sharp and metal wedging itself into his bones. Gaster pressed down on the plunger a bit slower than usual, and as soon as the last of the red fluid had emptied, he pulled the needle out, set it on the table, and looked back up.

It took less than a minute for Papyrus to grit his teeth, squeezing his eyes shut and clenching his hands into fists. Gaster looked away. At first he had tried to force himself to watch, to make himself see what he was doing. But it wasn’t helping anything. It wouldn’t make the experiment finish any faster, and it wouldn’t make it any less painful for Papyrus.

The best thing he could do for his son was to get this done. As quickly as possible.

Then they could go back the way things had been before.

But far, far better.

Gaster wasn’t watching the clock, but he estimated that around five minutes passed with Papyrus sitting in that chair, gritting his teeth, several whimpers slipping past his throat as he squeezed the arms of the chair almost hard enough to snap them off. He had screamed a few times early on, but apparently the pain had lessened since then—or he had gotten used to it. It didn’t make those five minutes any easier. After those minutes had passed, the tension in Papyrus’s body began to fade, and a minute later, his pushed himself to his feet, shaky, his eyes still hazy when he forced them open.

He turned to the wall, his hand trembling as he brought it up from his side.

Gaster watched and waited.

But no bones appeared.

His browbone furrowed. Papyrus’s hand lifted further, his face tight with concentration, determination, even though he didn’t want to do this, he still did it, he was dedicated, he was loyal, he wasn’t like his brother, he would _never_ give up—

Then Gaster saw the shape forming over Papyrus’s left shoulder.

Faint at first, fading into existence like a bone attack, but larger. Much larger. Almost as larger as Papyrus itself, except it was wider, thicker, and it …

It was … a skull.

Not a skull like any of theirs. It looked a bit like he might have imagined the king’s skull looking like, only far larger, and more sinister. It stared ahead with empty sockets, yet gave off the uncomfortable sense of awareness. Gaster shuddered.

It was an attack. It wasn’t alive.

But before he could think anything else of it, it opened its jaw, wider than any skeleton he had ever seen.

And a burst of light shot from its mouth, piercing the air and blasting straight into the wall in front of it.

Papyrus jolted back as the blast impacted, just in time for a flash of white light to overtake the whole room. Gaster couldn’t see, couldn’t hear beyond the sound of debris, the crushed stone falling to the ground, the smoke that filled the air. He waved his hand in front of his face, struggling to make out the damage, where’s Papyrus, he was in that, did he get hurt, it was his own blast, he wouldn’t have—

The smoke faded, bit by bit, and Gaster could see the charred wall across the room. Papyrus stood just a few feet away from where he had stood before, his arms tight against his body, his eyes wide and locked on the scene before him.

“Did … did _I_ do that …?”

It sounded like a child’s voice, small and distant and so filled with shock it barely came out as full words. And Gaster almost didn’t hear it, his eyes focused on the increasingly-visible wall, the damage, the surface completely scorched, the stone chipped away, the smoke still clearing where the blast had hit.

“Yes,” he breathed. “Yes, you did.”

Papyrus drew in a sharp breath, and Gaster could hear him taking a few steps back. “That’s … that’s horrible … you said there’s no one around, right? No one got hurt, did they? You didn’t get hurt, right?”

“There’s no one here, Papyrus,” Gaster muttered, unable to keep the tinge of irritation from slipping into his voice.

Why was he so focused on that? Gaster had told him there was nothing to worry about, couldn’t he _see_ what he had just _done,_ what the S.E. had _allowed_ him to do?

Gaster strode across the room to the wall, hesitating only a moment before running his fingers along the scorched stone. It had withstood everything he had thrown at it over the years. It had held up against corrosive chemicals, stray bone attacks, and a few things he still didn’t have a name for even now that several decades had passed. But this attack … it was still standing now, but Gaster had little doubt that a few more blows of the same caliber would leave it damaged beyond repair.

He had never seen an attack like that. Papyrus was strong, he had known that, his attacks had always been _impressive,_ but nothing like this. If only four doses of S.E. could do _this_ …

He had to do more tests. Figure out exactly what these blasters were capable of, figure out how exactly the S.E. had changed Papyrus’s magic, whether it had changed his _soul._ Humans had never used the same kind of magic as monsters, and the humans that had fallen had shown no signs of magic at all, so there was no way to compare in that sense, but something this powerful, something that did this much damage in a single blow, when he had never _heard_ of a skeleton using any sort of attack that didn’t involve bones or gripping someone’s soul—if that didn’t indicate a significant change in someone’s soul, Gaster didn’t know what could—

“I don’t like it.”

Gaster stiffened, and it took him a second to recognize the voice speaking just behind him. He turned around to find Papyrus still watching him, his hands squeezing the hem of his shirt, his head held high even as his mouth pressed into a tight, trembling line.

Then the words clicked. Gaster blinked.

“What?”

“I don’t like that thing,” Papyrus repeated, glancing over his shoulder, even though the blasting skull—he needed to pick a name for it soon—had long disappeared. He gripped himself tighter. “It was … why would I ever want to use something like that?”

Gaster just stared, even as Papyrus turned to face him again. The words wouldn’t register. They didn’t make sense. What would he _do_ with it, what _couldn’t_ he do with it, with an attack like that, Gaster knew Papyrus had never been particularly _prided_ himself on his physical strength, but with something like this …

If Gaster had had something like that, all those centuries ago, if he had had that during the war …

He had been strong, then, certainly, but far from the strongest. He had been young. Inexperienced. Afraid.

Unwilling.

So many of them had been unwilling.

If he had had those blasters, if he had fired them off instead of standing there like an idiot watching as his brother’s HP fell those last few points …

“Dad?”

Gaster looked back up, slower this time, blinking to shake away the thoughts clouding his head as his eyes focused on Papyrus again. Papyrus stood a bit straighter now, still shaky, still unsure.

“I … I don’t like this.”

“What?” Gaster breathed, still trying to make sense of the words coming out of his son’s mouth.

“I don’t like any of this,” Papyrus repeated, more assured. He shifted from foot to foot. “This … I thought we were supposed to be doing tests to break the barrier. We’re not going to blow the barrier up with that attack, are we?”

For a second, a split second, Gaster wanted to snap at him for how stupid that was. Then he stopped, the words frozen in his throat, and swallowed them, forcing his face to smooth out where it had begun to wrinkle.

“No. The barrier can’t be blown up.”

“Then why are we doing this?” Papyrus asked, his voice lilted up.

Gaster let out a long breath through clenched teeth. His hands curled into fists, but by sheer force of will, he stretched them out again. He looked at Papyrus and felt himself frowning despite his best intentions.

“I thought you wanted to help me, Papyrus.”

“I do!” Papyrus cried, almost before Gaster had finished speaking. His eyes flashed with such desperation it almost hurt to look at, before he stared at the floor, fidgeting, wringing his hands almost tight enough to twist his own fingers off. “But … but … you’re … different. You act different. You’re always so focused on these experiments, and I know you did that a lot before, but you never ignored me and now you do and sometimes the experiments hurt a lot and I want to tell you that they hurt but you don’t even look at me and I don’t want to lie to Sans but I do, every day, and he’s worried, he’s _scared,_ but I can’t tell him anything and I don’t like it, I don’t like this, I don’t want to do experiments like this but I want to help you and I …”

He swallowed and shook his head, not looking back up. Gaster stared at him. Just stared, taking him in, and for a second, just a second, he wanted to run across the room and pull him into his arms and hold him and tell him all of this could end.

But … that would be giving up.

And if he gave up … neither of his sons would ever see the surface.

Papyrus wanted to see the surface. He wanted his _brother_ to see the surface.

Just because he was a little … hesitant, that didn’t mean he wanted to _stop._

He couldn’t stop. _They_ couldn’t stop. They had to keep going. They had to keep trying.

“I need you for this, Papyrus,” he said, before he even realized he had opened his mouth. “I can’t do this by myself. Your brother is … unable to help, and we … we’re close, I know it, what you did today, what those injections _allowed_ you to do, that will move us forward. We can get there. But we can’t do it if you back out now.”

Papyrus looked back at him, his sockets wide, his shoulders hunched, his hands squeezed so tight in front of his torso that he looked ready to snap one of them off its wrist.

“dad …” he said, his voice fainter than Gaster had heard it in years.

Gaster pressed his mouth into a thin line and took a deep breath. He turned away before the image of Papyrus’s eyes could burn itself into the back of his head.

“I’m going to repair this wall and fortify it further,” he went on, his voice as plain and scientific as he could ever remember hearing it. His face softened as he looked at the wall, at the damage, at the proof of how far they had come, the proof of how far they _would_ go. As long as they continued. “Then I need you to summon that blaster again.”

Papyrus’s feet shuffled against the floor, but it was a faint sound. Distant. Irrelevant.

“I …”

“Please, Papyrus,” Gaster breathed, looking over his shoulder just enough to meet his son’s eyes.

Papyrus stared at him, but Gaster didn’t let himself focus on his expression. He couldn’t. If he was going to finish this, if he was going to get through this and get everyone out of here, keep everyone safe, give his sons everything they deserved … then he couldn’t let himself be distracted. He couldn’t let himself be deterred. Papyrus had agreed to this. And he would be fine. Once they got out of here, he would be more than fine.

Gaster watched his shoulders fall, watched his head tilt until he stared at the floor.

“okay.”

Gaster closed his eyes, opened them again, and nodded, before turning back to the wall once again.

Papyrus stayed in the lab while Gaster examined the wall, while he took his notes and planned out the next tests to be done, but he didn’t look at him for the rest of the day.

Gaster did his very best not to notice.

It would be worth it. Soon, with just a little more work, it would all be worth it.


	23. Chapter 19

**Notes for the Chapter:**

> Haven't said it here in a while, but seriously, thank you so much for all your kudos and comments, everyone. :D Now for the chapter ...

Sans was well aware of his tendency to get lost in his work, so he made sure to set an extra-loud alarm to go off at four in the afternoon. Normally leaving at five would have been plenty of time to get him back to the house, but that was just if he wanted to make it home for dinner.

Today was special.

Or, rather, he was going to _make_ it special.

When the alarm buzzed, he forced himself away from the T.F. machine, stacked up all the papers he had collected that day, gathered the rest of his things, and left his private lab.

Usually, leaving the lab felt like leaving something exciting. Especially since his dad had been so quiet lately and hadn’t been much for conversation, and Papyrus … Sans still hadn’t figured out what was going on with him. Even though Sans felt, in a way, like he was abandoning his family when he went to the lab, it also felt like an escape.

Here, he had control over everything. Here, he knew exactly what was going on, what he was doing. He could see progress every day he worked.

Here was where he renewed his energy to deal with the rest of his life.

But now, even as he locked the door behind him, he smiled—more than the constant smile that never left his face.

Maybe he couldn’t fix everything with his dad and his brother. But a special dinner, with all three of them together, couldn’t do anything but help.

They hadn’t had restaurant food in a while, and Sans’s added paychecks were bringing in more than enough money for him to treat his whole family to a nice dinner. Papyrus deserved a break from cooking for them every day, and besides, Sans couldn’t remember the last time all three of them had been together for a meal.

Finally telling his dad about the progress he had made in his research would just be the cherry on the iced chocolate cake.

He walked a little faster, with more energy than he had felt in a while, different than the sort that had buzzed through him on his first day of work. For a second, he could actually believe that it _was_ his first day of work and he was heading to the main lab, even though it was the middle of the afternoon and he was coming from the opposite direction. It was nice having his own place to work, to plan his own projects and focus on what he found most important.

But it wasn’t what he had expected. And it was lonely. Alphys came by now and then when he invited her, but she did most of their collaboration work from her house, and aside from her, he spent his days alone.

Yeah. A family dinner would be good for all of them.

He had to spend a few minutes digging out his key card from his work bag, and for a second he was afraid he would have to call his dad to let him in, but finally he found it, tucked in the very bottom. Had it really been that long since he had used it? He slid it through the reader, heard it beep, then walked through the doors as they opened. He could have just gone home, told Papyrus the plan, and waited for his dad to come back. But it had been far too long since he had visited his dad in his workspace, and frankly, he wanted to see whether his dad had actually found a project to fill his time.

The elevator doors opened when Sans was only a few steps into the room, and a monster almost as tall as his dad stepped out, her furry, pointed black ears perked up as she adjusted her bag over her shoulder and started out into the ground-floor lab.

As soon as she saw him, she stopped dead, and a second later, her whole face lit up in a grin.

“Sans!”

Sans’s smile stretched all the way across his cheekbones, and he lifted his hand in a wave. “Hey, Dr. Japes, it’s been forever!”

Despite her age, Dr. Japer crossed the room in a matter of seconds. From the excited gleam in her eyes, he might have thought it had been years since he had last seen her, rather than a few weeks.

Then again, she had always seemed to think of him as a nephew, and though she treated him with the utmost professional respect, she never stopped looking at him with the sort of pride he might expect from a favorite aunt. Maybe he should have expected it, given that she had known him since he was a baby. He had seen her look at her actual nephew with just as much affection as she did him.

“I heard you were working in your own private lab now,” she said, crossing her arms once she stood in front of him. “Fancy!”

Sans shrugged and rubbed the back of his skull.

“Yeah, my dad set me up with it. Why, you guys miss me?”

“It’s just been so quiet here lately,” she said, shaking her head. “I hardly ever see your dad anymore. He just comes in every morning and locks himself in his lab. I know he’s not the most social of monsters, but he must have started something really big. I haven’t seen him this into his work in years.”

Sans paused. His smile slipped, just a bit.

“Yeah, I … thought he might be working on something new, but … he’s really that busy?”

If she noticed his change in tone, she gave no sign. “Mm. I’m glad your brother’s keeping him company, though.”

Sans froze. He stared at her for a moment, trying to make sure he had heard her right. But there was no reason he would have heard her wrong.

“What?” he managed.

“Your brother,” she repeated, her smile unaffected by his blatant confusion. “I’ve seen him coming in at least three times this week. Maybe more, he can be quiet when he wants to be. I guess he comes to bring him food, even though he seems to stay for a while. Dr. Gaster’s a lot like you in that respect, he tends to forget to feed himself in the middle of a big project.”

She winked, then sighed and shook her head in long-held fondness. And before he could think to say anything else, she patted him on the shoulder.

“Anyway, I’d better get going. I promised my brother I’d help Lin with his homework. You take care of yourself!”

Sans nodded blankly, and she flashed him one more smile before slipping past him. He stayed perfectly still until the lab doors closed behind her.

He paused there for another minute, just staring, his browbone furrowed and his thoughts tilting back and forth. Then he forced his feet to move again, carrying him into the elevator. He pressed the button and leaned against the wall as the elevator began to descend.

Well, he hadn’t been here in a while. Maybe his dad had gotten some new idea while he was gone. Maybe he had taken up the icy bracelets again—as much as Sans made fun of it, it _was_ a viable idea, if he could work out all the kinks. Besides, this was what Sans had suspected, wasn’t it? And this would explain it. Maybe his dad had finally thought of something worthwhile of taking his time. Maybe he had gotten his passion back. Even if it occasionally came with some unpleasant consequences, Sans had never seen his dad happier than when he was in the midst of an exciting project.

This was a good thing. He knew it was a good thing.

But that didn’t explain …

The elevator doors opened, and Sans walked out just a little faster than usual.

He didn’t stop. He didn’t think about it any more than he already had. Everything was fine. He was sure of that. But his feet still moved a little faster, his mind bouncing from side to side, seeking out an explanation that made any sort of logical sense.

When he reached the door, he didn’t bother to knock. He never knocked. He just grabbed the knob, turned it, and pushed the door open.

“Hey, Dad, I—”

Sans stopped.

His mind shut down.

His dad stood across the room, in front of one of the examination tables. The same examination table Sans had lain on himself, the table that might as well have been his bed for those few weeks, cold and metal and sturdy enough to hold him no matter how hard he thrashed about.

But the table had something on it.

Something tall and thin and white with eyesockets that widened as they landed on him and a jaw that opened as if to speak even though no words came out.

His brother.

His brother, lying on the table.

As his dad tightened a strap around his arm, pinning him down.

None of them moved. None of them spoke. Sans’s dad stared at him, his sockets as wide as Sans had ever seen them, his mouth just open enough for him to make it out across the room. Sans could barely see Papyrus’s expression for the angle he was lying at, but he could see his eyes, locked on him, almost as stunned.

His dad’s browbone tilted up near the center in something like sadness. He opened his mouth.

But before a single syllable could slip past his teeth, Sans lifted his hand, gripped his dad’s soul, and threw his arm to the side.

His dad flew across the room, crashing into one of the machines and Sans panicked, he had attacked his dad, that was his _dad,_ he had hurt him, how could he do that, _why_ would he do that, how could he—

Then his eyes fell on Papyrus again.

And he moved before he could think.

He crossed the room in just a few seconds, his hands scrambling for the straps almost before he had stopped moving. Papyrus, have to get him out, get him out of here, can’t let him—he could see a little table in the corner of his eye, the same little metal table he had seen when he lay here like Papyrus was, with a scalpel sitting in the middle, the same scalpel his dad had used to—

The same scalpel his dad had promised he would _never_ —

“Sans—”

Papyrus was talking, but Sans didn’t listen. His hands worked, unhooking each of the straps in turn, refusing to meet Papyrus’s eyes even as he felt his gaze burning into his head.

“Sans, it’s okay! I-it’s okay!”

No. Not okay, not okay, _never_ okay.

He … his _brother,_ he …

His dad had …

The last strap came loose just as Sans heard the shifting of bones against metal off to the side. He didn’t have time. He grabbed Papyrus’s hand and yanked him to his feet, fast, too fast, it must have hurt, but he had to get him out of here, he had to get him away, get out of here, get away from _him._

From their dad.

From their …

Sans squeezed Papyrus’s hand and ran out through the door of the lab, turning right down the hall and scrambling away just as he heard the first faint groan from far behind him.

He didn’t know where he was going. He didn’t think. He didn’t even hear what Papyrus was saying, why was he talking, what was he saying, they just needed to _run._ So Sans moved, as fast as his legs would carry him, even as he wondered whether or not this was just an elaborate dream, because this couldn’t be real, how the _hell_ could any of this be real, he had promised, he had _said_ he wouldn’t, and now—

Sans turned into the first room he passed aside from a closet, pushing the door open and slamming it shut behind him.

Only then did he finally let go of Papyrus’s hand.

Papyrus was still talking, but Sans wasn’t listening.

He looked around him, taking in their surroundings, his mind coming back to life as the pieces clicked. The papers covering the nearby desk. The anatomy textbooks stacked up on another table. The mug that read “Best Intern Ever,” right next to the one that read, in sloppy red handwriting, “Coolest Boss.”

Sans gritted his teeth.

He was an idiot. He didn’t care about his degree or what people said about his age, he was a _complete idiot._

Dr. Frewth’s lab. He couldn’t think of anywhere else to go but _Dr. Frewth’s lab_?

He couldn’t keep him out. His dad knew this lab better than Sans ever would, he had been working here before they were born, after all. And he would be closer now, no time to run, Sans’s head swung from side to side even as Papyrus shouted his name, trying to get his attention.

His eyes fell on the chairs by the desk—Dr. Frewth always had guests, always had too many chairs—and without pausing to think, he scrambled across the room, snatched one of them, and carried it back before lodging it under the knob of the door. It wouldn’t hold long, he _knew_ it wouldn’t hold long, but neither would anything else.

And he needed time. Any time he could get, any time to process what the hell was going on, any time to _begin_ to understand what he had seen back there—

“Sans?”

Sans jolted, stepping back from the door even though the voice from the other side was barely audible through the wood. He bumped into something and spun around to face Papyrus, who stared down at him with wide, worried eyes, his mouth open as if he might speak, though no words came out.

His brother.

His brother who had had marks on his bones.

His brother who had insisted he had just “tripped.” His brother who had been far quieter recently than Sans had thought he was even capable of.

His brother … who his dad had …

“Sans,” his dad said, and that was his voice, that was his _dad’s_ voice, was he imagining this, was this all some elaborate nightmare, because there was no mistaking that voice, no one else in the entire _underground_ talked like that. No one else spoke to him with that kind of affection. Sans heard a faint sigh from the other side of the door. “I know how this must seem to you—”

“Oh, _do you_! ” Sans spat, everything that had built up inside him bursting all at once. His limbs trembled, and it was all he could do to keep his eyes on the door and not start pacing. “Well, then, tell me. What _is_ it, ‘cause I sure as hell know what it _looks like_! ”

His dad didn’t say anything for a few seconds. Sans could just make out a hint of a sigh.

“I understand you’re disturbed, Sans, but please, just listen to me.”

Sans gritted his teeth and squeezed his shaking hands into fists. “Why? Why the hell should I listen to you when you didn’t listen to me? I told you it was too much, I told you it _hurt,_ I told you I wanted to stop, and you just _dragged Papyrus in to take my place_? ”

“He offered, Sans.”

Silence. None of them breathed, none of them moved, none of them spoke.

Sans let out the air already gathered in his ribcage, and his hands couldn’t seem to decide whether they wanted to squeeze tighter or go limp.

“What?” he murmured.

“He offered,” his dad repeated, in a quiet, reasonable tone Sans had never hated so much. “I told him what was going on, what we needed to do, and he volunteered for the experiments.”

Sans stayed perfectly still for a few seconds, staring at the door. He could feel Papyrus fidgeting just out of his line of sight, but he didn’t turn to look. His head wasn’t working right, and he couldn’t figure out whether his mind was making him hear things that weren’t real.

“You’re lying,” he snapped, taking a step back from the door without removing his eyes.

But he wasn’t lying. Sans knew he wasn’t lying. He knew it far too well, he could imagine Papyrus in the lab so easily, jumping at the chance to help, at the chance to do something important, something to help all of monsterkind.

Just as eager as Sans had been. More so, probably.

Because he had no idea what he would be getting into.

And Papyrus never gave up. On anything. Once he started something, he saw it through to the end.

No matter what.

“Then ask him,” his dad said, with no pleasure, no audible smirk. Just quiet facts.

The same tone he had used before he pressed a button and sent an electric shock straight into Sans’s soul.

Sans turned around, very slowly, slowly enough that maybe something would happen before he had the chance to finish. But in what felt like half a second, his eyes were on his brother, standing to his left, maybe two yards away, watching him with wide sockets, his mouth pressed into a tight, wobbly line.

“pap?” Sans breathed, even as his shoulders began to sink.

Papyrus looked down and gripped the hem of his shirt, shifting his weight from foot to foot.

“I just want to help everyone, Sans,” he said, more forlorn than Sans could ever remember hearing him. “That’s what Dad’s trying to do, isn’t it? Get us out of here. And … and he said we’re getting closer! it’s okay, really, it doesn’t hurt that much.”

He looked up and smiled, a shaky, hesitant smile, a smile that didn’t last long when he looked at Sans’s face.

Sans’s body felt like it had turned to stone, every bone frozen in place, his curled fists trembling from how hard they clenched.

“You _agreed_ to let him _experiment_ on you?”

Papyrus stepped back, but a moment later he lifted his head, just a bit, his eyes not quite accusing, but pinning him in place nonetheless. “so did you.”

Sans stiffened, and his soul squeezed in his chest.

“What?”

“He was doing this stuff to you before,” Papyrus replied. It wasn’t a question, and there wasn’t a tad of uncertainty in his voice, even as he fidgeted more. “you let him do it. You … you wanted to help, too. That’s why you did it. Right?”

Sans blinked, once, hard, but when he looked again, Papyrus was still standing there, and Sans had just heard the exact same thing. He stared closer, his sockets painfully wide, his arms going limp at his sides. “and you didn’t … this whole time, you …”

Papyrus’s eyes softened, just like they always softened, so gentle and concerned and innocent and _god he had been hurting so much and Sans hadn’t done a damn thing._

“Dad said it hurt you too much, and that’s why you stopped,” Papyrus went on, hesitant yet hopeful. “but … I’m … I’ve always had a lot of HP. I can handle it. And if I’m doing it, we can still get to the surface. And … you won’t have to get hurt anymore.”

Sans couldn’t breathe. He stared at his brother, taking in every inch of him. The marks from weeks ago had faded by now, but … how long had those circles under his eyes been there? How long had his shoulders hunched so much, how long had he been fidgeting every few seconds, as if he couldn’t bear to stay still?

How much had Sans missed?

How long had this been right in front of him, and he hadn’t seen it?

How many times had he brushed it off as he went to work, thinking that whatever it was, he would deal with it later?

How many times could he have stopped it, if he had just …?

Sans’s limbs trembled, his sockets burned, his breath caught in his throat every time he tried to get air in. And Papyrus just looked back at him, apologetic, gentle, but so, so hopeful, as if he could still solve all of their problems if he took what Sans couldn’t take.

If he stepped in when Sans had been too afraid.

The beginnings of words formed in Sans’s chest, and they bubbled up, one by one, until the first hint of a syllable slipped past his teeth.

Then the door flew open.

Sans spun around, his eyes wide, his soul clenched, his hands in the air, ready to fire off another attack. But the instinct didn’t come like it had before. And by the time he could make out the vague shape of his dad, he felt the pressure of magic wrap around his soul and hold him in place, lifting his feet just enough off the ground for him to hang in the air, kicking and thrashing helplessly.

He focused his energy, raised his hand for another attack, but the pressure on his soul tightened until his magic fizzled out and refused to gather. Shit. Shit shit shit shit _shit._ He had forgotten about that. He had read about it a dozen times, he had just never _felt_ it, never thought he would ever have _reason_ to feel it.

Skeletons were the only monsters who could grip souls directly.

So there was no reason for Sans to learn how to defend against the ability.

Not when his dad had only ever used it to move him out of the way of danger.

Not when he had sworn he would never use it strongly enough to block Sans’s magic.

He wanted to scream. He wanted to cry and flail, he wanted to throw a fit, but he could barely move, even lifting his limbs was a struggle. His dad stepped further into the room, and Sans barely registered him lifting his other hand until he was holding Papyrus in place as well.

Not as firmly. Papyrus wasn’t fighting.

He was just staring at the floor, glancing up at Sans, pained and scared, but resigned.

Like he had already long accepted this was how things were going to be.

What the hell had Sans _missed_?

His dad looked at him, and Sans stopped moving, staring back at him, begging, _pleading,_ even though he couldn’t get out a single word. Even though his mind was failing him. Even though he couldn’t understand one iota of what was going on. His dad said nothing, just looking, his mouth pressed into a tight line and his sockets wide and shining.

And for a second, just a second, he actually looked sad.

Then he closed his eyes and sighed, turning his head away.

“I’m not enjoying this, Sans,” he said, his voice as tight as the grip he held on Sans’s soul. “This is the most painful thing I’ve ever done.”

Sans tried to make himself say he was lying. But he wasn’t lying. Sans could see it on his face. He could see the crease between his eyebrows, the pinched line in his mouth, the pain gleaming in his sockets when he opened them again.

“But I don’t have a choice. If the only way to protect you, to give you a chance at a safe, better life is by … is by hurting you, then I’ll do it.”

Sans thrashed against the grip on his soul, even though he knew it was useless. He may not have been weak, but his dad had always been stronger. And he had centuries more practice honing his natural skill.

“How is this protecting us?!” Sans spat, though it came out far more pleading, far more desperate, as his eyes fell on his brother’s pained face. “How is hurting both of us protecting us?”

“I’m getting us out of here,” his dad said, looking back to him at last, sockets wide. “You’ll be _safe_ on the surface. You could have _died_ in that cave-in, Sans. What if something worse happens?”

Sans froze. His sockets widened, and it took his mind a few seconds to even comprehend what he had heard.

“Is that what this is about?” he breathed. His dad’s face remained the same. “It was just a freak accident! We’ve been fine down here for _centuries,_ the mountain’s not just gonna collapse on us!”

“Are you sure about that?” His dad straightened, his fingers curling inward, a reflex that made his grip on Sans’s soul just a bit tighter. His face set. “You’re nineteen, Sans. You haven’t seen a _fraction_ of the suffering everyone has endured down here. If something happens to us in this cave, we have _nowhere_ to go. We’re stuck here. We’re scavenging through the garbage just to find what we need to survive as it is!”

“And the garbage keeps coming! We’re not dying down here, we can wait! The king’s already got five human souls, two more and we’ll be out!”

His dad stared at him, silent, for a few seconds longer. Sans tried to remember a time when his face had looked like it did now. He found nothing.

“The last human fell before either of you were born,” his dad replied, after a long silence. He gritted his teeth. “It took _centuries_ for the _first_ human to fall, a soul we didn’t even get to _keep_. We could be stuck down here for another thousand years, and neither of you will _ever_ get to see the sun!”

His words hung heavy in the air. Sans barely noticed the grip on his soul anymore, and Papyrus lifted his head, his browbone raised, sockets wide. Their dad’s head fell, and his hands clenched at his sides.

“You’ll never get to see the world they stole from us.”

He stood there, perfectly still, completely tense, before his shoulders drooped, and he lifted his head again, his eyes gleaming with something that made Sans’s soul shake.

“I can get us out,” he said, and he hadn’t sounded so sure of anything, so desperate, since he had finished the Core. “You saw the results, Sans, and I have more than three times the information now. Once I’m done, we can go back to how things were. No one else will have to get hurt.”

Sans didn’t say anything. He didn’t know what he _could_ say, he couldn’t make his voice work, he couldn’t move, he couldn’t _think._

His dad looked at them, then let out a long breath and shifted his hand toward him. Papyrus, pulled by his soul, stumbled to his feet and followed their dad toward the door, his eyes wide in a swirl of emotions Sans could no longer read.

“Use me instead.”

The words fell from Sans’s mouth before they had even registered in his head. His dad and Papyrus froze, turning their heads to face him, both of their browbones furrowed in such perfect mimics of each other it made Sans shiver.

“What?” his dad asked, very quietly.

“Sans?” Papyrus asked, barely softer than his normal volume.

“Use me for the experiments!” Sans went on, louder this time, holding himself straighter despite the weight pulling down on his chest. “We both have the same kind of soul, you can use either of us, so use me!”

Papyrus’s browbone shot up. It had been years since Sans had seen him quite so afraid.

“Sans!”

“I can’t do that,” their dad said, before Sans could say anything else. He looked at Sans, his eyes somewhere between clinical, factual, and sad. “These experiments require the subject to be as durable as possible, and they’ve gotten more … intense since you stopped. Papyrus has several times your HP. He can withstand these experiments safely, but you?”

“I’m not made of glass!” Sans spat.

“But you’re not as strong. And I won’t risk you dying just because you wanted to play the martyr.”

He looked away. Probably for the best. Sans wasn’t sure he could take the pained look in his sockets. After a few seconds of silence, he sighed.

“Papyrus will be fine,” he went on. He turned to his right, expression softer, even though the crease in his browbone remained. “Won’t you, Papyrus? You’ve already withstood a great deal and you’ve helped me very much.”

Something boiled in Sans’s soul, and he thrashed his arms and legs, his good eye burning with enough magic to make it light up. “Don’t you _talk_ to him! ”

“You’re strong, Papyrus,” his dad said, as if Sans hadn’t spoken at all. He smiled so gently, how many times had he smiled like that and _meant_ it, could he actually mean it now, how could he make Papyrus hurt and still _look_ at him like that. “You’ve helped me and you’ve helped your brother and now you can help save everyone.”

“ _Shut up_! ” Sans screamed.

Papyrus put his hands to the sides of his head, whimpering, looking between Sans and their dad in desperate confusion. Their dad just looked to Sans again, his smile gone, his eyes pained, his breath quiet when he let it out again and tugged Papyrus closer still.

“I’m sorry about this, Sans. Please believe me, I am more sorry than I’ve ever been about anything in my life. But I have to keep going, and I can’t risk you stopping me.” His grip on Sans’s soul tightened, just a bit, as he lowered him to the ground and nudged his soul closer to the door. “Come on.”

Sans found himself stumbling forward, following his dad as he pulled the door open and led both him and his brother into the hall.

“Where are you going?” Sans stammered, despite his best attempts to keep his voice steady, his head jerking between the back of his dad’s dead and Papyrus at his side. “Where are you taking us?”

His dad didn’t even turn around.

“I’ve already set up this experiment and several of the tests I have prepared for the results won’t last if I wait until tomorrow. Normally I don’t want to rush these things, but this won’t wait. We need to complete this tonight. Then you can both rest. You can have the whole day to sleep in tomorrow, but we must finish this now.”

Sans knew that tone. It was the same reasonable, logical tone he had heard so many times over the years, when he and Papyrus sat around in the background while their dad worked on one of his projects. Not cold or overly scientific.

Just stating facts.

With a pained look in his eyes, as if someone were forcing his hand.

“Dad!” Sans shouted, his voice choking off before he could make much of a sound. “dad, stop it, just … do you even hear what you’re saying, do you even see what you’re _doing_ to him, you’re hurting him, you’re—”

“He agreed to it,” his dad cut him off. Gently. Achingly. As if he would have changed it if he could. As if he hadn’t _chosen_ it, with the full ability to choose something else. He looked at Sans, he looked at Papyrus, then he looked away and sighed. “It’s for the best. It’s for the best for both of you.”

Sans tried to think of something to say. _Anything_ to say, he couldn’t just agree with this, he couldn’t just—let him pull him along and—

“Papyrus has been generous enough to do this for me. He _can_ do this for me, and I will make sure that everything he has done matters.”

Sans bit back the whimper growing in the back of his throat. He looked to his brother, begged him to speak up, begged him to say he didn’t want to do this anymore, that was all Sans had to do, ask him to stop, maybe it would work again, maybe it would work this time, maybe he would listen, maybe he would stop and they could go home and forget about this, Sans would forget, he would make himself forget, he had forgiven his dad last time, he would forgive him again, he just wanted it to—

“Please, Sans,” his dad went on, so gentle, so pleading it hurt, even as he kept his eyes turned away. “I know this is difficult for you to understand, but this is what’s best. You know I would never do something like this unless it was best for you.”

Sans jerked in his dad’s grip, but the pressure on his soul remained. “You said we were your sons. Not your experiments, your _sons_! ”

The hold on his soul tightened. Not with anger, not with any intent to cause him pain. Like he had squeezed him when he almost fell over the edge of a cliff in Hotland and into the lava below.

“And that is exactly why I have to do this.”

Sans couldn’t speak. He couldn’t think. And he couldn’t do anything but stare as his dad started out of the room and down the hall, dragging him and Papyrus along behind him.


	24. Chapter 20

**Notes for the Chapter:**

> Things aren't going to go very well from here. At all. You have been warned.
> 
> Just to be clear, Sans is not meant to be completely rational in this chapter. He’s panicking. He’s terrified. People don’t always make their most rational choices when they’re panicked and terrified.

His dad didn’t let go of his soul the whole way back to the lab.

And Sans never stopped struggling.

He cried out a few times, when he thought of it, partially in protest and partially in the vain hope of getting someone’s attention. But nobody ever heard. Nobody ever came. Everyone else in the building had already gone home. There was no one around to hear them.

And Papyrus, who could have screamed loud enough for Snowdin to hear him if he wanted to, never made a sound.

Their dad refused to look at them, keeping his eyes ahead and his face almost blank as he dragged them down the hall. Every few seconds, his face twitched, as if he could barely hold back a wince. But it never made it through. And by the time they neared the familiar double doors, his expression had hardened completely, and he tugged them even faster than before down the darkened hallway toward his own lab.

But just before he turned the final corner, he stopped.

Sans didn’t notice the closet door to their right until his dad had jerked it open and pushed him inside.

He crashed into the brooms and buckets and mops piled up in the corners, his skull slamming straight into the wall. His head spun, but he still managed to flip himself around, scrambling to look at his dad and Papyrus, Papyrus’s eyes wide, his hand outstretched in concern, as if to help Sans back up.

For a second, Sans swore he saw overwhelming guilt flash across his dad’s face.

Then it was gone, and his mouth set as his eyes shifted away.

Sans pushed himself to sit up, though his dad’s renewed grip on his soul kept him from standing completely.

“what are you doing?” he managed, holding back the tremor in his voice. His teeth gritted, and his browbone set. “what are you gonna _do_ to him?!”

His dad still refused to meet his eyes.

“He’ll be fine, Sans. This is hardly a risky experiment, he’s gotten through far more intense. He’s stronger than you, and he has a high pain tolerance,” he replied. He looked at him, just for a second, long enough for Sans to see pain that he could almost believe was real. He looked away again. “I’m sorry, Sans. I really am. I swear I wouldn’t be doing this if there was any other choice.”

“You always have a choice,” Sans said, hardly louder than a breath.

His dad’s hands curled into fists, and Sans felt the squeeze on his own soul as painfully as he saw Papyrus wince, though their dad didn’t seem to be paying attention to either of them.

“Not if it means keeping those I love safe.”

His face smoothed out, and he held his head up again, staring at a spot in the closet just above Sans’s head.

“I don’t want to keep you locked up, but if you’re just going to try to stop me, there’s no other option. This work is essential, Sans,” he went on. His mouth pressed into a thin line, and just as his grip vanished from Sans’s soul, his newly-free hand rested on the door. “I’m sorry. We won’t be long.”

Sans scrambled forward, arm reaching out toward Papyrus, toward his brother, his brother, _watching him with pain in his eyes he was going to get hurt again and_ —

“dad! dad, please, _stop it_! ”

The door shut. The lock clicked.

And Sans sat frozen as his dad’s footsteps tapped away down the hall.

He threw himself forward, slamming into the door and banging his fists against the wood. He screamed so hard his throat hurt, pounding his hands until his HP began to fall from the damage, pausing only long enough to breathe before he screamed again. But nothing happened. No one heard him.

Nobody came.

Papyrus. _Papyrus._ He had Papyrus, he was going to hurt Papyrus, he had already done all those things to him, he had done _worse_ than he ever did to Sans, he had _already hurt him and he was going to hurt him again and Sans couldn’t get out and—_

He summoned bone attacks and went after the door, again and again, but all it did was wear down his magic faster. The lock never budged. And the building was empty. He could make as much noise as he wanted, but no one would hear him. No one would come to help.

He panted, his vision blurred—no, there was something in his eye, his eyes were wet, tears, when had he started crying?—his head spinning as a whine slipped past his teeth. This wasn’t happening. This couldn’t be happening, this couldn’t be _real,_ it was ridiculous, it was a nightmare, it seemed real, yeah, but dreams _always_ felt real when you were still inside them.

Right? Didn’t they? He couldn’t even remember.

It took him more than a minute to realize that his own whine had quieted.

And another sound, distant, muffled, and far, far more painful, had taken its place.

Screaming.

 _Papyrus’s_ screaming.

That was … that was …

Sans banged his fists one more time against the door, and only noticed the tears streaming down his cheekbones when they plopped down onto his knees.

This couldn’t be happening. But …

How? How the hell had this happened without him knowing? How long had it been going on? That guilt on his dad’s face when Sans called him out on what he was doing, that had been genuine, hadn’t it? Had he gone straight to Papyrus once he realized Sans was no longer willing? But … he had agreed, both of them had agreed, using Papyrus in these experiments was out of the question, right from the beginning, so when had he even started to _consider_ …

This was his dad. His _dad,_ making Papyrus scream when Sans knew he could endure quite a bit more pain than most monsters. If Papyrus was hurting bad enough to _scream_ …

His dad could hear it. He hadn’t gone deaf, he could _hear_ Papyrus screaming and he _wasn’t stopping_ and _when the hell had this whole stupid experiment been worth putting Papyrus through so much agony_ —

_“If it could get us all out of here … it’s worth whatever I have to go through.”_

He had said that, hadn’t he?

Sans had said that. He had spent so much effort convincing his dad that this research had been worth starting in the first place, that it was _worth_ a little pain, and his dad had _believed_ him, even if it had taken a long time. He had agreed with it, reluctantly, then avidly. Agreed with it enough to keep going even when Sans was suffering.

Agreed with it enough not to notice that he _was_ suffering.

But he had changed his mind, hadn’t he? That horror when Sans had told him how much he hated this, how much he wanted to stop, that hadn’t been fake, had it? He had closed the drawer on that experiment, literally, and left it behind. He had spent days quieter than usual, consumed with guilt no matter how hard Sans tried to alleviate it.

That _had_ been guilt, hadn’t it?

Sans knew his dad had been disappointed they couldn’t move forward with the research, that the barrier would remain unbroken, but …

This was still his dad.

His dad, who had never laid a hand on either of them, in however small a way.

His dad, who, for all his faults, had done everything in his power to assure that neither of them were ever hurt. And if they were, that they were cared for as quickly and effectively as possible. So much so that Sans had once worried that his paranoia over them getting hurt was aging him even faster.

When Papyrus cracked his leg, his dad had been the one to break down in tears, afraid that he had failed them both—even if he tried to hide his panic when he knew they were watching. He had fretted over the smallest injury, the briefest tear, even if it was over literal spilled milk. He had done everything, throughout their entire childhoods, to ensure that they were healthy, happy and safe, as if anything short of perfection would make him a failure as a parent. The only area where he hadn’t immediately corrected himself was how little time he spent with them … and he had still fixed that in the end, too.

So how the _hell_ was that same man making Papyrus scream now?

What had happened? What had changed? The rockslide? Had that really shaken him that much? No, of course it had, and Sans _knew_ it had, but he didn’t expect “shaken” to look like _this._

It hadn’t been that long since all of this had started, had it? It had only been a few months, right? A few months wasn’t enough to change someone beyond repair. Not with what had happened here. His dad … the man he grew up with, the man who raised him … he couldn’t just be gone, right? He was in there. He _had_ to be in there.

He couldn’t be gone. Not like this. Not this fast.

Sans could get him back. He _had_ to get him back.

He just … he had to …

What could he do? His dad wasn’t listening to anything he said, but it had only been, what, an hour? Less than that. Was he beyond convincing? Would anything Sans could say get through to him?

What about someone else? Dr. Japer? His dad had always listened to her advice, maybe _she_ could convince him.

But …

What would she do, if she found out what was happening? She cared for his dad, sure, but … she had always been like an aunt to them. She was _still_ like an aunt to them. She thought so highly of his dad now, but if she knew about this … she would tell someone. She would make sure he stopped. And Sans _wanted_ him to stop, he wanted more than _anything_ for him to stop, but …

If she told someone else … if _everyone_ found out …

Would his dad be arrested? Taken away? Would they give him a chance to go back to the way things were before? Sans had never heard of anyone in the underground actually being put into prison, he knew _about_ prisons, but they didn’t really _have_ prisons down here, did they? Was what his dad was doing a crime? Would Sans be able to get him out once he was put in?

If someone else found out … they could lose him for real. Forever.

No. He couldn’t let that happen, Papyrus would never forgive him, he would never forgive _himself._ This was bad, but he could handle it. He could do this. He just had to _think._

Papyrus was screaming, and Sans couldn’t tell whether or not it was just in his head.

He couldn’t get help. And he couldn’t change his dad’s mind. Well … maybe he could, he could keep trying, but … how long would it take? How long would Papyrus continue to suffer? And what if it didn’t work?

He was persuasive, sure. But he couldn’t count on his own persuasion skills for this. If his dad was convinced enough of the importance of getting them out of here that he would willing to put Papyrus through torture …

But what else could he do? If he couldn’t go to someone else, and he couldn’t count on his own ability to convince his dad, and Papyrus, Papyrus wasn’t fighting back, he _could,_ he was strong, he could fight back if he wanted to, maybe he wasn’t as strong as their dad—was he? It wasn’t like the two had ever fought—but he _could_ fight, it just obvious that he _wouldn’t._ Not if he had let it get this far.

There had to be something else. There was _always_ something else, there was always an answer, he just had to keep trying, there was always another way …

He huffed a laugh, even as tears continued to stream down his cheekbones, and his hand curled into a fist. Would his dad have come this far, if he knew what Sans was working on? If he knew that he was researching timelines, parallel universes, if he knew that if Sans got far enough, he might be able to get them out of here with his own research? It might not be fast, but he was _working_ on it. Was it too late to convince him?

It …

Sans’s browbone furrowed, and his hand spread out against the door.

Timelines.

That was what he was researching. Timelines. The interaction of space and time.

He had been focused on parallel universes, looking side to side, but … timelines went backwards and forwards, too. They did it all the time. Well, forwards, anyway. And they were already _here,_ in _this_ timeline. Looking into another timeline might take months or years more research, but _this_ timeline …

If he could measure the timelines … if he could focus his research on _this_ timeline … could he find a way to travel within it?

It seemed ridiculous, at first thought. Time travel was the sort of thing he had been fascinated by when he was a kid, the sort of thing that kept him reading his sci-fi novels under the covers long after Papyrus had gone to sleep. The sort of thing he had dreamed, in his early years, of accomplishing, before he took his first physics course and learned exactly how far-fetched the idea actually was.

He still dreamed about it, from time to time. But it had never been a priority. Not when there were so many other things he _could_ do, things that were more within his immediate reach, things that he could quantify and study. That was why he had written his thesis on the idea of spacetime: something measurable, even if it was still invisible, something that would stretch the limits of hard science but not rely solely on theory.

It had been years since he had considered actually _doing_ something with his pipedream.

Time travel into the future was easy—theoretically, at least, even if he doubted they would have the technology for it for centuries. Time travel into the past …

And that was what he was thinking about, wasn’t it? Going into the past. To do what? To convince his dad not to start experimenting on his brother? What was he supposed to do, waltz in and tell him he was about to make a huge mistake and hope that worked?

Could he even affect the past? That had been one of his pet projects just before he started college, the theories of how time travel would work if it could be achieved. Would he go back to the future and find it changed? Wouldn’t that create a paradox? If his dad never screwed up, Sans wouldn’t have to go back into the past to _stop_ him from screwing up. Maybe the present was set in stone and he couldn’t change it at all, maybe he already _had_ gone back to the past and he was destined to do so to create the present he lived in now, but that brought up all kinds of questions about free will and the nature of the universe and—

But there had been one other theory. One of Sans’s favorites, the only one that held up to most of the questions he could throw at it.

If he went back to the past, and he had the free will to change things, the universe had to have some way of preventing a paradox.

So as soon as he went back … the timelines would split.

One where he hadn’t gone back, and one where he had.

Parallel universes.

And that _wasn’t_ a pipedream. That _wasn’t_ pure theory anymore.

It wasn’t confirmed, certainly, but there was no other logical explanation of those readings. Parallel universes already existed.

So if he could go back in time … go back early enough, find out when things had fallen through, create a parallel universe where …

Could he do that? Even if he could, _should_ he? If he created a parallel universe, sure, things would work out in _that_ universe, but what about in this universe? Would it keep existing? Would he just … disappear from this universe? Would he abandon Papyrus to his dad’s mercy—or lack thereof?

Were there any other options?

A faint scream reached him, just a little louder than before, and Sans pressed his skull to the door and squeezed his sockets shut.

He didn’t even know if it was possible. He didn’t know if … but he …

If he couldn’t stop it any other way …

If he could perfect the theory … if he could design a machine with enough power, if he could _figure it out_ …

Sans didn’t move for a long time after that. He listened, and he let the ideas settle in his head, fitting into place just as they did for every project he had ever taken on—even if he had never taken on one even a fraction of the size of this.

He didn’t notice the sound of the door opening and closing in the distance. He didn’t notice the footsteps until they were just outside the door, and he only pulled away a second before the door disappeared from under his skull.

He looked up, and found his dad standing just outside the door, his gaze focused off to the side, angled toward the floor.

Papyrus stood just behind him, off to the side, still in view, but hunched over, taking up as little space as possible given his lanky body. He wobbled every few seconds, as if he couldn’t quite stand straight, and Sans could see his bones trembling. Papyrus should never look so small. He should command attention in any room he walked into, bright and happy like the sun Sans had never seen, and might never see until the day he died.

It was dark, the lights in the hall dimmed, and Sans’s eyes had yet to adjust, but he couldn’t see a single mark on Papyrus’s body. Not a single physical sign of whatever had caused every one of those screams.

How many times had he come home looking tired, defeated, but without a single physical mark?

How many times had Sans overlooked it?

How many times could he have done something about it, if he had just paid close enough attention?

His dad didn’t say anything. He didn’t even look at him. He looked … tired. Almost as tired as Papyrus, and the guilt that had flashed across his face several times before was more obvious now. But he wasn’t apologizing. He wasn’t saying he was going to stop. The guilt was there, much heavier now, but it came with none of the remorse that suggested he was going to try to do better.

He wore the look of a man who hated what he was doing, but was going to do it anyway, because it had to be done.

Sans’s legs ached when he stood, and he barely managed to keep himself up without falling. His dad didn’t rush him, or even acknowledge his struggles, though Sans swore his fingers twitched as if to reach out every time he swayed. Sans stepped out of the closet, and his dad closed it excessively gently before starting back down the hall.

He didn’t grab hold of either of their souls, but both Sans and Papyrus followed without a word or a nudge, their heads low, their footsteps in almost perfect sync.

None of them spoke as they rode up the elevator, or walked back through the ground floor of the lab. It would have been so easy to slip away. In the distracted state his dad seemed to be in, Sans doubted that he would even notice if they disappeared, as long as they were quiet enough. But neither of them did. The thought barely even crossed Sans’s mind.

It wasn’t until they were halfway back to the house that his dad finally cleared his throat.

“I … hope I won’t need to do this again, Sans,” he said, and there was such pleading, such pain in his voice, that for a second, Sans felt guilty. Like all of this would have been fine if he hadn’t made such a big deal of it. Then his head snapped up, and his mind whirred back to life, just as his dad continued, wringing his hands close to his chest and keeping his gaze ahead. “It’s not something I enjoy. I don’t want to keep you … Sans, the idea of locking you up is horrendous to me. I hope you know that.”

He tilted his head over his shoulder, as if to meet Sans’s eyes, though he still kept his gaze off to the side. Sans didn’t say anything. His dad pressed his mouth into a thin line, closed his eyes, and turned his head forward again.

“But I need to be sure that you won’t interfere. I can’t let you prevent me from helping you both. From helping everyone.”

Sans wanted to scream. He wanted to blast his dad to tiny bits, he wanted to squeeze all those words out of his throat, but he couldn’t speak, he couldn’t lift a hand, he couldn’t do anything but walk forward. His dad sighed, and for a second, he turned just enough to meet Sans’s gaze.

“Please, Sans,” he breathed. “I want to be able to trust you.”

Sans lowered his head to stare at the ground, and he wasn’t sure whether he wanted to slink into a corner and curl up into a ball or shove his dad into a lava pit.

Then both feelings slipped away, and Sans just walked as his dad let out a heavy breath and turned his head the other way, toward Papyrus on Sans’s right.

“I’ll make you some tea before you go to sleep, Papyrus,” he said, gently, and Sans didn’t have to look up to hear the shaky smile in his voice. As if Papyrus hadn’t been screaming less than twenty minutes before. As if he was still the same man who patched up their every tiny scrape like their life depended on it. “It should help you recover faster. You can sleep in tomorrow. We’ll need to do some follow-ups, but we can wait until late morning.”

Papyrus didn’t say anything, but nodded, a tiny nod with a tiny, shaky smile to go with it. It was the worst expression Sans had ever seen on his brother’s face. Even worse than when he cracked his leg.

Their dad smiled back, a hesitant, yet affectionate smile.

Sans wanted to die.

But he couldn’t die. He couldn’t … he had to stay here. He had to fix this. He had to do whatever it took to make sure that Papyrus didn’t have to suffer anymore.

That his dad …

It wouldn’t be easy. And it wouldn’t be quick. His dad wasn’t just going to let him go back to his lab right away. Not while he still thought that Sans was going to betray him. He would have to wait it out, wait for his guard to lower, wait until he could sneak away without attracting suspicion. He would have to pretend, pretend that he was going along with it, even if he couldn’t pretend he was okay with it.

He had to make his dad believe he wouldn’t go to someone.

His dad wasn’t stupid. He wasn’t just going to buy it if Sans suddenly “changed his mind.” But …

… his dad wanted to trust him. Sans could see that, as clearly as he could see anything. He wanted to believe that Sans was on his side. Or, rather, that he was still on Sans’s side.

And if Sans could be convincing enough to convince him to give him just a little bit of leeway …

None of them said anything when they reached the house and stepped inside. Their dad went to make Papyrus some tea, just as promised. Sans wanted to grab Papyrus’s hand and drag him upstairs and hide him in his room and keep him there for as long as he could. But Papyrus stayed in the living room, waiting for their dad to finish the tea, and Sans found his legs carrying him up to his room and shutting the door behind him.

There was nothing he could do. Nothing to help Papyrus.

Their dad wouldn’t do anything while they were at home, would he?Would Papyrus know he could come into Sans’s room if he wanted to?

After who knew how long of suffering through it alone …

Sans waited for a while, just standing there in the middle of the room, listening to the faint sounds from the rest of the house. He heard the kettle whistle. He heard the muffled sound of talking from downstairs—almost all his dad’s voice. Then he heard footsteps, one set, then another, climb the stairs and go into their rooms.

He should have gone out there. He should have gone after his brother and stayed with him through the night. He should have made sure that he never had to be alone after …

But he also should have made sure that none of this happened in the first place.

Sans found his feet carrying him to his bed, and felt himself collapse on it before he knew what he was doing. He didn’t bother to change into nightclothes. He just adjusted himself over the blankets until he finally slipped underneath them, tugging them up to his jaw.

The lights were still on. He didn’t feel like getting up to turn them off.

He stared at the opposite wall and fought against the warring urges in his mind to scream and to never move again.

Neither was going to do his brother any good.

“I’ll save you, Papyrus,” he breathed, so quietly he could barely make it out, even in the silence of his room. He ducked his head further under the covers, gripping the blankets so hard he could feel his fingers trembling, the fabric almost tearing under the force of his grasp.

He squeezed his eyes shut and swallowed back the last of the tears in his throat, locking them away and tossing the key far, far away. Tears wouldn’t help Papyrus. Tears wouldn’t change his dad’s mind. He pulled the blankets far over his head, feeling the warm darkness encircle him, cradling him in an illusion of safety he would never believe again.

And he let the images of his brother smiling flash behind his eyes, his laugh, his irritated scowl, his soft eyes when he hugged Sans and told him he loved him and was proud of him and he was the best brother in the world.

Sans’s breath hitched, but no more tears came.

“I promise.”


	25. -11

**Notes for the Chapter:**

> Kind of cracked up when both of you requested babybones, RandomCat1832 and CaitieLou. Here you go. XD
> 
> One thing to mention before continuing with the chapter: despite what may go on in Sans’s internal monologue, please remember that _Sans is not a reliable narrator_. He blames himself in part for what happened with Gaster, but that doesn’t mean it’s actually his fault. Did he push Gaster to start the experiments? Yes. But Gaster is still a two-thousand-year-old adult while Sans is his nineteen-year-old son. Gaster should have known when to stop (or, in this case, not start in the first place). He’s the parent, and he needs to be the responsible one and make better choices. Which, obviously, he didn’t. And in the case of Papyrus, as much as he may tell himself that Papyrus offered himself up as a test subject willingly and freely, he _did not fully disclose the risks_ , and even if he had, he still should have refused knowing how bad the tests would get.
> 
> No matter what drove him to it, he still had the choice as to whether or not to hurt his kids. He made that choice. No one forced his hand, no matter what he may claim. It is still his fault. There are ways in which Gaster was a wonderful dad (at least before), and there are many other ways in which he was (and is) a terrible one.
> 
> Also, though I haven't gone into that aspect of the story as much yet, Gaster still had a lot of issues before the experiments began. The experiments just brought those issues out.

He couldn’t do this.

He had thought he could. He had spent the last eight years, every single day, trying to prove that he _could_ be a good father, that he _could_ take care of the two precious boys that had resulted from a stupid lab experiment.

But he couldn’t.

He should have known that from the beginning. He _had_ known that from the beginning. He had just been too stubborn to listen to his own common sense.

Gaster had never been cut out for fatherhood, as much as he had tried to convince himself—and everyone else—otherwise. He had dedicated his entire life to his work, to his research, to his projects, and even though his whole life had been turned upside down from the moment he found those two tiny skeletons in the mason jar in his lab, he couldn’t change who he had made himself into.

He had never had a family. He had never _planned_ to have a family. There were no other skeletons to start a family _with,_ not a biological one at any rate, and besides, that sort of thing had never interested him much in the first place. He had never put much value into family activities, or any activities that didn’t involve experimenting and taking notes. Even in the first few months of their lives, Gaster still found himself jotting down notes on their development that sounded a little more like scientific observations than they did the usual baby milestones. If not for Dr. Japer, coming over every few days to give him tips, to help him, to make sure both he and the boys were still faring alright, who knows whether they would have grown up half as happy as they had so far?

If not for everyone else …

He had gotten better. He would give himself that much. But he seemed to learn the essentials of care for each age group only after the children had moved on to the next stage, and he had to learn everything all over again.

He had thought it would get easier when the boys started school. He wouldn’t have to worry about their safety in the lab when he took them to work with him. But instead he found himself twice as likely to get into lab accidents, consumed with worry over whether they were safe, happy, whether the other children were nice to them, whether they liked their teachers. It took only a few weeks for it to become clear Sans was out of place among his classmates—while they were learning the alphabet, he was reading high-school-level astronomy textbooks—and then he found himself coming to the school even more often, talking with the teachers before they finally decided to let him work at his own pace, at least to an extent.

Gaster would have suggested he be moved ahead, to be with children learning closer to his level, but Sans wanted to stay with his brother, and Gaster wasn’t about to deny him such a simple request.

Especially when Papyrus had … a bit more trouble making friends at first.

He managed it, with time. He was so inherently kind that Gaster couldn’t imagine why any child wouldn’t want to befriend him. But he had spent very little time around other children until now, and just like Sans had to adjust to being far more advanced academically than his classmates, Papyrus had to adjust to his classmates not accepting all his quirks as easily as his family.

And just as the boys finally began to settle in, the energy problem arose.

It had been arising for some time, of course, but no one had paid much attention to it. It was easier to ignore until it became a pressing problem, and it became clear that old-fashioned methods of power were quickly running low. The king asked the entire underground to limit their power usage, and though there was some grumbling, everyone complied—at least after the first incident of all power failing because the power plants had been temporarily drained.

But being stringent with power use wasn’t going to solve the problem forever. It would delay the inevitable, but it wasn’t going to keep them from running out of electricity. And though it would technically be possible to go back to living the way they had been before, lighting their way with candles and bioluminescence—Gaster had spent centuries functioning that way—many monsters had grown up with modern technology, and they weren’t going to take losing it very easily.

No one had asked Gaster to fix the problem. But no one had ever had to ask Gaster to do anything.

And less than a week after the announcement of power conservation, he was already sketching out designs for the Core.

It hadn’t crossed his mind, at first, how busy that would make him. Even in the sketching stage, he found himself staying longer at work, sometimes even forgetting to go pick up the boys from school until one of their teachers called him. It wasn’t until he discovered that he had forgotten to make breakfast three times in a row—and Papyrus had taken up the task without complaint—that he forced himself to keep reminders for the essentials on sticky notes around his room.

Get the boys ready for school—and feed them.

Pack their lunches.

Take them to school.

Pick them up from school.

Make them dinner.

Eat dinner.

Help them get ready for bed.

He got those things done without fail from then on. The new problem arose when those were the _only_ things he would do with the boys, and aside from that, his attention was focused on the growing designs for the Core.

Then the design was approved by the king, and construction began.

And Gaster realized exactly what he had gotten himself into.

He was home for dinner, certainly. That was one thing he made sure of, except if there was absolutely no way to avoid it—which usually meant there was something in the lab that would explode if he left it by itself for five minutes. Even if he could give them nothing else, he would always spare half an hour to eat dinner with the boys.

But other than that?

He was there in the morning, usually. At the very least, he made sure there was someone else there to make the boys breakfast and get them to school safely. But even when he was there, he often wasn’t paying attention to them. He jotted down ideas while he microwaved a frozen meal for breakfast. He was lost in his thoughts on the way to their school. He picked them up thanks to the alarm on his phone, but he was still scatterbrained, and often found himself eager to get back to work. So eager that, far too often, he forgot to even ask about their day.

Dr. Japer still came by to help now and then, but Gaster tried not to ask her if he could avoid it. Though her niece was a good deal older now, her brother had had another child two years ago—a boy this time, with orange fur and far too much energy—and Gaster knew she was trying to spend as much time helping out with him as she could.

It wasn’t fair for him to depend on her again.

Alphys was busy with all her studies—and with her early high school graduation, only a year away now, from what he had heard—but she was still happy to come by and help whenever he asked her, mainly because she could usually entertain Sans while she was doing her homework and Papyrus was happy as long as she gave him a few minutes of attention every half-hour or so. And as her school was right next to the boys’, all it took was a text to ask her to pick them up if he couldn’t make it to the school himself.

Today had been one of those days.

He had only planned to stay in the lab one hour more. Just one hour, long enough to finish his current experiment. He hadn’t thought he would need to set his alarm to remember it. He had thought he would be home in plenty of time to cook them a nice meal, something other than leftovers and the frozen dinners Papyrus clearly hated.

He didn’t look at the clock until he felt his phone buzzing in his pocket.

And he didn’t process the time until he read Alphys’s text telling him she had to get home, and asking whether she should call another babysitter to take over.

He typed out his response, telling her to go ahead and get back home, as he was shoving his notes to the side and pulling on his coat.

He was out the door within a minute, shoving the phone in his pocket and starting back in a brisk pace toward his house.

He spent the first few minutes cursing himself for his own stupidity, and the rest of the walk simply staring at the ground.

It wasn’t going to get better. Not anytime soon, anyway. Work on the Core was well underway, but it was a big project. A _very_ big project. It would be another year, at least, until the Core began producing steady electricity, and another few years after that before he had it stabilized and automated enough not to spend all day working on it.

How many years would it be until he could keep that promise he had made, five years ago in his lab?

How old would the boys be before he could spend the time with them that they deserved?

How long would it be before he could be the father that he had told himself he would try his very best to be, when he pulled them out of their tube?

It had been eight years, but he still had no idea what he was doing.

Perhaps … would the boys better off with someone who actually _did_?

Someone who had expected to be a parent, who had prepared for it, who hadn't gone into this whole venture blind because it had only hit him the moment they were born that he _couldn't_ let them go?

Had that been selfish of him? Should he have given them up to someone more competent? Had he even been thinking of the children when he decided to take them in rather than give them to someone else? Or had he just been thinking that he couldn't bring himself to say goodbye to these two precious little lives, who rested their heads on his chest and clung to his clothes and cuddled against him just as fervently as they cuddled against each other?

Was he selfish to still look forward to every hug, every skeleton kiss, every drawing, every word, every breath, every _second_ he could spend with them?

Even now, as he saw his house appearing in the distance, he couldn’t help but feel relieved. It was a different kind of relief than he remembered from his time living alone. It hadn’t even been relief then: most of the time, he would have gladly stayed in the lab all night sleeping in spurts while he worked on whatever project currently had his attention. Home was … the place he kept his things. The place he went back to when he couldn’t stay at the lab any longer. The place where he could be alone for a while if the lab was too busy.

He had never had anything to look forward to, when he got home. And the boys had given him that.

Had he given them anything in return?

He stepped onto the porch and pushed open the door, and before he had a chance to look around, two tiny skeletons had latched themselves around his waist.

Tiny, yet not nearly so tiny as he remembered.

When had they had time to grow this much?

They were smiling, as they always did when he first got home. They talked over each other, neither seeming to notice that the other was already telling the story of what they had done at school that day, how much fun they had had with Alphys when she came over to babysit, and asking what they were having for dinner that night. It was the same thing they did every day, and Gaster found himself smiling despite himself.

He could never seem to remember whether his workday had been good or bad once he got home. Once the boys started talking, their day was all that mattered.

Yes. He was selfish, without a doubt. Yet he couldn’t imagine being able to stop.

The boys were hungry, so he put some leftovers in the oven to heat up. Again. When was the last time he had made a real meal for them? Even the leftovers were simple, quick things he threw together in five minutes. Papyrus had been asking for cooking lessons on the weekends lately, though—he had been making simple, no-cook meals since he was five, and he had long mastered the waffle-maker for quick breakfasts—so that might change in the near future. Gaster still wasn’t sure how he felt about the boys using the stove when he wasn’t home, but … well, Alphys would be there. And she was responsible, despite her nervous temperament. At the very least, she wouldn’t let the house burn down.

He stayed in the kitchen as the leftovers cooked, staring at the oven as if it might give him all the answers he wanted. He didn’t hear the clack of two sets of skeleton feet on the floor until they were right beside him, and even then, he stared forward until a little hand tugged on his sleeve.

“Daddy?”

Gaster blinked, then looked down to find Papyrus and Sans standing just to his right, Papyrus holding his hands behind his back.

“Yes, Papyrus?” he asked, though his eyes shifted to Sans as well.

Papyrus and Sans looked at each other, then back to him. Then Papyrus brought his hands out from behind his back and held them out toward Gaster.

“We made you something.”

Sans nodded, and before Gaster could process what he was seeing, he reached out and took the small, thin object in careful fingers. He looked down.

It was … a card.

Or something very similar to a card. A piece of thick paper folded in half, decorated with what he suspected were the same crayons he had picked up at the store a few weeks earlier. On the front, he found a stick-figure drawing of him and Sans and Papyrus, their arms around each other, smiling at him, and inside he found a note, scrawled in familiar, careful, bright red writing.

_We love you, Daddy._

_Sans and Papyrus_

“Sans did the drawing, and I wrote the words.”

Gaster could barely bring himself to look up at Papyrus’s voice, and he hardly noticed Sans lowering his head and shuffling back and forth, hands behind his back, like he did when he was embarrassed.

“Sorry the drawing's kinda bad,” he murmured.

Gaster’s fingers tightened around the card, and he forced himself to loosen his grip before he wrinkled the paper. He looked at them, then back at the card, then back to them and back to the card, several more times until his stubborn mind finally got it.

“Sans … Papyrus, you two … you ...”

Papyrus fidgeted, smiling, though the smile was more than a little shaky. “Do you like it?”

Gaster opened his mouth, but no words came out. He tried again, and again and again but nothing sounded right in his head. Nothing could encompass the warmth growing in his chest, spreading through every one of his bones, making his head swirl with a rush of overwhelming _love._

He had lost count of how many times he had felt the exact same thing. He didn't think he would ever get used to it.

Just as Sans looked at him again, his face fallen, ready to speak, Gaster dropped to his knees and pulled both boys into a hug almost tight enough to crack their ribs.

The boys stiffened, just for a second, as if in surprise—how long had it been since he hugged them, that they would be _surprised_?—before squeezing him back, just as hard. They clutched each other in a messy pile of bones, so close they risked getting tangled up together, but Gaster didn’t care. He would have gladly stayed there for hours, just holding them, how had he not realized how much he missed this, holding them close, feeling the warmth of their bodies, the thrum of their souls, the precious lives he had brought into the world?

But after several minutes, despite his reservations, he finally pulled back, looking between the card and his sons with soft eyes.

“So you like it, then?” Papyrus asked, his voice slightly more high-pitched as he eyed Gaster with wide sockets. “Right?”

The thin line of Gaster’s mouth trembled as he struggled to hold back the trembling breaths that threatened to burst from his throat. Bit by bit, he smiled, his own eyes brimming with the beginnings of tears.

“It's the most beautiful thing I've ever seen.”

In perfect synchrony, the boys beamed, exchanging a brief, triumphant glance before looking back to him.

“Are you going to put it on the fridge?” Papyrus went on.

“Oh, goodness no,” Gaster replied, before he even had the chance to think. Papyrus’s face fell. Gaster smiled, gentle yet tight with emotion. “Something this important deserves a spot on the wall. I think I may have an empty frame around here. If not, I'm sure we can find one.”

He looked down at the card again, at the carefully-written message, at the little drawing that was, without a doubt, the best Sans had ever made, especially since Papyrus had always spent far more time on artwork than his brother. His whole face softened.

“Something like this should be preserved properly.”

“So you’re not going to put it on the fridge?” Papyrus asked, and only when Gaster turned to face him again did he see the blatant disappointment written all across his face.

Gaster tilted his head. “Do you want me to put it on the fridge?”

Papyrus looked at Sans, who looked back to him, before they both turned to face him again with small nods.

“You said all the best art goes on the fridge.”

Gaster laughed out loud before he could stop himself. Papyrus and Sans stared, sockets wide, browbones high. Gaster’s fingers tightened once again around the drawing, and he barely managed to keep himself from crumpling it by accident.

“Well, then,” he said, smiling even wider than before. “How about I find a nice frame for it, then put it up on the fridge? Does that sound like a compromise?”

Sans looked at Papyrus. Papyrus looked back. After a few seconds, Sans turned to Gaster again and nodded, faint stars in his eyes.

“That's good.”

“Yeah!” Papyrus added, his face even brighter than his brother’s. “That means you really like it!”

Gaster chuckled again, and allowed himself one more lingering look down at the drawing. He could imagine the two of them on their fronts on the living room floor, crayons scattered around them. He had been a parent long enough to tell a scribble from an intentional drawing, and this had been crafted with care. The positions—Gaster in the middle, Papyrus on his left, Sans on his right so his good eye was closer to them—the clothes—Gaster’s old lab coat, Sans’s fuzzy jacket he had gotten on a trip to Snowdin, the red boots Papyrus had found in the dump. And the smiles. Even in stick figures, Gaster could see the warmth of Papyrus’s expression, and the eager grin that always adorned Sans’s face when he found a new challenge to focus on.

And Gaster’s, gentle and loving.

Was that what he looked like?

Was that how they saw him?

Even when he was late from work, even when he didn’t have as much time to spend with them, even when he was forgetful and distant, even when he should have done _so much more_ for them, even when they deserved so many things he might never be able to give?

He looked at his sons. His _real_ sons, looking up at him with wide, expectant eyes.

His sons who loved him, despite all his faults.

Gaster smiled, fully, unabashedly, his eyes as soft as they had ever been.

“Yes, Papyrus. Yes, I do.”

And as they beamed up at him, with more pure joy than he had seen on anyone’s face in all his life, he felt the last of the tension in his soul slip away.

He would find a way to make this work.

They were worth it. They were worth everything. And no matter how difficult it got, he had taken on this challenge, and he was going to see it through to the end. He was going to give them the life they deserved.

No matter what it took.


	26. Chapter 21

**Notes for the Chapter:**

> Watch those tags, everyone. Particularly manipulation and depression. And cursing, though that's not a tag. No suicidal thoughts just yet, but later ...
> 
> (And as always, thank you so much.)

It was like someone had drawn a line through Sans’s life.

On one side was everything he remembered. Everything he cared about. Everything he loved. His family, his career, his hopes and dreams.

And on the other side was … this. Whatever “this” was supposed to be.

It had been just over a week, but Sans found it harder and harder to remember what before was like at all.

Maybe it just hurt too much to remember. Maybe it was just too painful to look at the man taking his brother out every day for experiments and remember that that was his dad. The same man who had carried them as children, who had bought them every toy they could ever want, whether they asked for it or not, who made them their favorite foods and played games with them and even when he messed up, he still did his best, and he _always_ tried to do better.

Maybe it was easier to pretend that that man was just … gone. Off on a trip. Maybe he’d gone on vacation. Maybe he’d be back soon.

Maybe the man who had taken his place would be gone the next day.

But every morning, he never was.

Sans wasn’t sure what time of the day was hardest. In the mornings, he woke up having forgotten what was going on. He woke up believing, just for a few seconds, that he would be heading off to the lab—his own lab or the main one, he didn’t care—and going about his day as usual.

It never took long for his head to remind him.

He always woke up before his dad and Papyrus left, even though he never set his alarm. He always made sure to be there to say goodbye to Papyrus, even though, at least half the time, he didn’t have any actual words to say. He wasn’t sure what he _could_ say. He was afraid that, if he opened his mouth, he would jeopardize all the time he had already spent building up a false image, and Papyrus would have to suffer even longer. So he said nothing.

He wasn’t entirely sure how his dad made sure he didn’t leave the house during the day. It wasn’t like Sans had tested it out to see what would happen. Maybe nothing would happen. Maybe it was all just a psychological trick.

Or maybe there really was some spell on the house, or a mechanism that would activate as soon as he opened a door or slipped out a window or threw enough bones into the walls of the house to break a hole through them.

Or maybe his dad just knew that he wasn’t willing to see what would happen if he broke out and told someone.

That was the problem with him knowing Sans as well as he did.

In any case, Sans spent the day in the house, pacing or staring at the wall or trying and failing to get actual work done, something that would speed things up once he was able to get back to the lab. He got some done. He managed a few designs, some basic blueprints, and a good bit of theory, jotted down on scrap paper and hidden away behind a loose board in the wall right behind his bookcase. Alphys had called twice, asking where he had been and if everything was alright, and he had spent a minute stalling her by asking about anime before he could come up with a half-decent excuse he still wasn’t sure she believed. Other than that, he had no contact with the outside world. He found things to do, even if his mind refused to stay occupied with whatever he was doing. He couldn’t just sit around doing nothing all day, as much as he couldn’t bring himself to do anything more than the necessities.

His bed remained unmade. His teeth unbrushed. He went days without changing his clothes, and while on some days he ate next to nothing, on others he gorged himself on everything in the fridge, making his dad wonder where all the food had gone when he got home.

But Sans paid very little attention to his dad when he got home—if he was even awake when his dad finally returned from the lab. On almost every day, Papyrus came home first, and once he did, everything that had consumed Sans’s mind for the entire day disappeared, only to refocus on the most important thing he knew.

It was never at a consistent time. Sometimes they would “finish” early, and Papyrus would come home early in the afternoon. Sometimes he wouldn’t wander in until nine in the evening, and their dad wouldn’t get home until past midnight. Sans always listened for the door, no matter what he was doing. And no matter how much his work absorbed him—which wasn’t half as much as it had before—he could always hear it.

Today, it was almost eight, and Sans had been sitting on the couch for the past hour, fidgeting, trying all he could not to imagine what the hell his dad could be doing that would keep them this late.

At 8:09, the doorknob finally turned, and Sans jerked around so hard he almost fell off the couch.

The tension in his shoulders fell, but did not disappear.

“hey, bro,” he managed, pushing through the tightness in his throat. Papyrus met his eyes, while Sans's gaze flicked over him, checking him even as he pushed himself off the couch and stepped closer. “how … how are you, um ...”

Papyrus smiled. There were no physical marks that Sans could make out, except for a bandage on the right side of his skull, the same one that had been there for the past two days. But his HP had fallen by more than half, and the dark circles under his eyesockets had grown larger.

As much as Papyrus went on and on about Sans getting enough sleep, he had never needed much himself. But now, Sans doubted that even sleeping for three days straight would do much to make him look less tired.

But still, Papyrus smiled.

“i’m okay, sans,” he said, very quietly, so unlike himself it made Sans shudder. Papyrus forced his smile a little wider, though it seemed to strain him to do so. “Don’t worry, I’m just fine. It only hurt a little bit, a-and I think we learned a lot, and … and ...”

Soul experiments, then. Those made up at least half, from what Sans had gathered. At first he had thought that his dad had just avoided the most violent of experiments so that there wouldn't be as much obvious evidence. But no, apparently most of the experiments were still a lot like what Sans had gone through, for however brief a time.

That had been near the beginning, though. And Sans wasn't sure he wanted to know how much worse they had gotten now.

He sighed and walked the rest of the way forward to lay a hand on his brother's shoulder and give it a careful squeeze.

“Come on, Pap. Let's get you upstairs.”

It was the same routine every evening. Sans led Papyrus up to his room, unmade his bed, and settled him in. If there were any physical injuries, ones that would be quick to heal, Sans would fix those up first, but tonight, he just dimmed the lights and went downstairs to the kitchen. He had never been much of a cook—certainly nothing like Papyrus, or even his dad—but he could make a few basic dishes, and tonight, it took him only five minutes to carry the overflowing bowl back into the bedroom.

Papyrus had settled a little further onto the pillow, but though his sockets drooped, he held them open, and as soon as Sans stepped inside and closed the door behind him, he turned his head to face him.

Sans tried to smile and held the bowl up for him to see.

“I made you cereal.”

For a second, Papyrus’s sockets widened like they had when he was a babybones and their dad said he was making waffles for breakfast. Then he paused and frowned.

“It’s nighttime,” he said, as if that were a complete answer all by itself. “You can’t have cereal at night, it’s for breakfast.”

Sans chuckled, even as his soul twisted and his eyes threatened to sting. “Well, we can break the rules just this once, I think. Besides, it's your favorite. I got the kind with the dried fruit."

Papyrus’s browbone shot up, and though he seemed to struggle for a moment, he finally leaned forward as if to peer into the bowl, even from the distance.

“Have they puffed back up yet?”

“Some of 'em,” Sans relied, smiling, even though it hurt. He stepped forward and held out the bowl. “Here, why don't you look while I heal you.”

Papyrus said nothing, but sat up a bit on the bed and took the bowl in both hands. While he stirred the spoon around and searched for the puffed-up pieces of dried fruit, Sans looked him over, checking where he should focus his energy, even though, by now, he had done this enough to already know. He took a deep breath and gathered all his magic into his hands. Then he settled them on Papyrus's chest, closed his eyes, and let the magic flow out into his brother's soul.

He must have healed a hundred times throughout his life. Papyrus, with all his energy, was prone to little scrapes and cracks, after all, and there was no point waiting for their dad to get home if Sans could heal him right then and there. It had never been anything bad, and it had never been difficult.

This wasn't like those scrapes and cracks.

The physical wounds, he probably could have handled fine. But injuries to the soul … was there a special type of healing for that? If there was, he didn't know. He wouldn't even know who to ask. All he could do was sit there and do his best to heal Papyrus just as he always had, by pouring every ounce of magic and love he could spare from his own soul into Papyrus's.

It had never been hard.

So why was he already so tired?

And Papyrus’s HP didn’t seem to be getting much higher. A little, sure, but usually it was a lot faster than this. And he _definitely_ shouldn’t have been feeling this worn-out if he hadn’t made much of a difference.

He paused, avoiding Papyrus’s baffled gaze as he turned his attention inward. He closed his eyes, searched for his soul, then for his level of HP, and—

6.

… what?

When had it … it had been low after the experiments, he knew that, but that had been _weeks_ ago, he had healed, he had recovered, his HP had gone up, he had _checked_ it, so when had it …

It was supposed to be 40. It had been 40 since he was fourteen, and it had always been at a decent level before that. When the hell had it dropped to _6?_

“Sans?” Papyrus asked, snapping Sans’s attention back to him. “Sans, are you alright?”

Sans stared for a second, trying to kickstart his mind. He shook his head, slowly, eyes still wide and voice breathy and quiet. “nothing, bro. Here, let me just—”

“No.”

Sans stopped and blinked. Papyrus laid a hand on his to stop him from moving any closer, and offered a small, reassuring smile.

“No, it’s okay. I’ll be fine.”

Sans’s browbone furrowed. He shook his head and leaned closer. “no, just let me—”

“You’re already straining yourself,” Papyrus cut him off. He was still smiling, but it was sadder now, his eyes soft and so wise that Sans wondered how he ever could have kept anything from him in the first place. “You don’t have to do any more.”

Sans tried to protest. He tried to think of every good reason that he should keep going, Papyrus was hurt, Sans had to heal him, but Papyrus just kept looking at him, _smiling_ at him, and as hard as he tried, Sans couldn’t manage a single word.

So, finally, he just sat back on the edge of the bed and stared at the floor.

Neither of them spoke for a few minutes after that. Papyrus ate the rest of his cereal, and made little sounds of approval that might have once made Sans feel happier just to hear. Now, he barely registered them. He just looked at his own hands, hands that had failed to heal his brother, he couldn’t do anything, he couldn’t help him, he couldn’t stop this, and now he _couldn’t even heal him._

Papyrus rested his hand on Sans’s shoulder and rubbed it every minute or so, and every time, Sans bit back a rush of guilt.

He wasn’t the one who should be comforted right now.

At last, Papyrus cleaned his bowl and set it on the nightstand, and Sans reached out to pick it up. He pushed himself off the edge of the bed, ready to take it downstairs and wash it. Maybe Papyrus didn’t want him here after all. It wasn’t like he was doing any good. Maybe …

“I don’t think he’s very happy with me.”

Sans stopped. He turned around, bowl still in hand, browbone furrowed.

“What?”

“Dad,” Papyrus replied, staring at his hands where they rested in his lap on top of the blankets. He wrung them together, and for a second he looked so much like their dad it hurt. “I don’t think I … I think he wants me to do something different. But I don’t know how.”

Sans had seen that face. He had lost track of how many times Papyrus had worn that face. Never when their dad was looking. Usually not even when Sans could see him.

The same face he wore when someone commented on how only one of their dad’s kids seemed to have inherited his intelligence, without realizing that Papyrus was standing close enough to hear.

Papyrus rubbed one of his hands over his other hand, a nervous gesture Sans hadn’t seen him do since he was twelve.

“I think he was hoping that … that something different would happen when he finished injecting the S.E. He said that it was helping before, but … I don’t think it worked as much as he wanted it to.”

He furrowed his browbone, as if trying to think of another way to put it, as if trying to understand anything about what their dad was thinking. But he said nothing else. And Sans just sat there, watching him, trying not to curse out loud.

Papyrus didn’t know much about the experiments. Or, rather, he didn’t _understand_ the experiments, he didn’t have the background, he hadn’t been studying these things for years like Sans had. But he had a good memory, and he could reiterate everything their dad had said, even if he preferred not to talk about it most of the time.

Sans had a good idea of what his brother had gone through before Sans had found him in that lab, about to get his soul sliced into. And that _was_ what his dad had been about to do. What he _had_ done, after he had locked Sans in the closet. He had done it before. Several times. Papyrus wouldn’t give him the exact number, and Sans couldn’t help but wonder whether it was because he couldn’t remember.

That wasn’t the majority of the experiments, though, at least from what Sans had been able to pry out of his brother. His dad had apparently already injected the rest of the nutrient fluid and all of the remaining S.E.— _pure_ S.E., not even diluted, if it had hurt like hell when he had given Sans the diluted stuff, how much must it have hurt Papyrus to get it straight?

But the last of those experiments had finished more than a week ago.

And even though his dad had kept his face carefully blank most of the time—when he wasn’t staring at one of them with soft eyes that made Sans want to scream at him until the entire underground heard—Sans still noticed him get tenser by the day.

“He’s been doing different things now.”

It wasn’t a surprise, even if Papyrus had never said anything about it before. Sans had hoped, very, very briefly, that once his dad finished everything he had planned, he would stop. Even if it didn’t give him what he wanted. Even he didn’t end up with the results he had hoped for.

Sans had hoped, had hoped so, so badly, that all of this would just turn out to be a fluke.

If experimenting on one of your sons and locking the other in a closet could be a fluke.

But he had still hoped. He would have let it go, probably, if his dad had changed his mind. He would have let them just go back to how things were. Even if he couldn’t forget it. Even if it would have haunted him for the rest of his life. If he would just stop hurting Papyrus …

But this wasn’t a fluke. It wasn’t a nightmare.

Sans looked at his brother and swallowed every angry word that forced its way up his throat.

“Like what?”

Papyrus looked away and shrugged. Even his shrugs looked different now. “He wants me to test those … blaster things a lot. The ones I told you about.”

“Yeah,” Sans muttered, forcing himself not to scowl. He hadn’t seen them. Papyrus wouldn’t describe them well enough for him to even get a good mental image.

It didn’t matter.

Anything that made his brother look so afraid wasn’t anything he wanted around.

“He was really excited about them at first. I didn’t like them, but … he seemed to think they were … important,” Papyrus went on, apparently ignorant to Sans’s growing anger. He fidgeted and frowned in thought. “He keeps measuring how much damage they do. He … seems happier when they do more damage.”

Sans tried to imagine the expression Papyrus had seen on their dad’s face. He tried to imagine how someone who had panicked over a cracked leg could possibly _enjoy_ seeing something destroyed, how he could ignore Papyrus’s fear. He still couldn’t get it through his head.

Papyrus swallowed hard enough for Sans to hear.

“They … do more now than they did before. When I first got them. He said the S.E. did that. But now that there isn’t any more … I think he’s hoping this other stuff will help.”

“Other stuff.” Did Sans even dare ask what that meant, other than testing the blasters?

He had seen the shift in his dad’s demeanor, even if he hadn’t been there to see the initial change. He had seen how the quiet, almost pained dedication, the certainty that this would all work out, had shattered further with each day that passed. He had seen the brief moment of weakness where he had hoped, he had pleaded to himself, that his dad would give up on all of this. That he would realize it wasn’t worth it.

Then he had seen the dedication return. The _determination_ return.

The certainty that even if he had no idea how he was going to get there, even if he had no idea how he was going to complete this experiment without any more S.E. to work with, he was going to finish this.

And he had seen Papyrus’s HP drop further every day since.

“He says he wants to make me stronger.”

Sans looked back up, slower than before, every inch he moved paining him as he caught a better look at his brother’s tense face. At the sort of expression he might have expected from someone who had failed at something important. Who had failed at something they were _meant_ to succeed at. Sans had never asked whether Gaster looked disappointed if his tests on Papyrus didn’t turn out the way he expected. He didn’t need to.

Papyrus’s face was all he needed.

His brother shifted in his bed, suddenly restless despite his obvious exhaustion.

“He said that I’m … not getting stronger because I’m rejecting it,” he went on, forming the words as if saying them might make him understand them more easily. “I want to do what he wants. But … I think he wants me to get stronger so I can hurt things. He doesn’t say it, but … there are a lot of things he doesn’t say and I know them anyway.”

He swallowed hard and glanced up at Sans before lowering his eyes to the sheets.

“i don’t want to hurt things.”

Sans choked on whatever words had been growing in the back of his throat. He rested his free hand over Papyrus’s.

“i know, pap.”

Papyrus stared at him for a moment before looking away again. Sans wanted to jerk his head back to face him, wanted to make him look at him, make him understand how wrong this was, make him understand that he never had to hurt things, he never had to hurt _anyone,_ he …

“He told me … that humans are destructive,” Papyrus went on, staring at the ceiling, thoughtful and confused. “They’re powerful and they destroy things. He said that … making me more powerful … like humans were … might make my soul more like theirs, too.”

Papyrus kept staring up, and Sans allowed himself a wince before smoothing his face out again.

How much had their dad forgotten, that he could think Papyrus could be anything like a human? That Papyrus could be filled with that same hate that trapped their entire race down here in the first place?

No matter what his soul was like, no matter how much human stuff had soaked in before he was born, Papyrus would never be anything like them.

If monster souls were made of hope, compassion and love, then Papyrus was more “monster” than anyone Sans had ever met.

But his dad couldn’t see that. Whatever was keeping him so dead set on this project wouldn’t let him. He couldn’t see that he was running after something he would never reach.

Something that would just hurt Papyrus even more.

Something that would _keep_ hurting Papyrus, that would just hurt him worse and worse and break his spirit and crush all his hope for the world and maybe that was what he wanted, maybe he thought that if he got rid of Papyrus’s hope he could get rid of the compassion and love, maybe he thought that if he hurt him enough he could make him more like a human, maybe he thought—

“please don’t be mad at him.”

It was so quiet, barely louder than a whisper, that Sans wasn’t sure he had really heard it at first. His head snapped up, and he found Papyrus staring at him, his mouth pressed into a tight, shaky line, his eyes wide and almost pleading. Sans blinked.

“What?”

Papyrus looked away. He looked a little like Alphys did when she was biting her lip, except Papyrus didn’t have a lip to bite. He fidgeted. “He … he doesn’t want to do this. He was … when it first came up, he really didn’t want to do it. He … I told him I wanted to help. I told him I wanted to help us all get out of here, I wanted to help him finish his research.”

He turned back to Sans, trying so hard to smile, even though every part of his expression trembled with the effort of keeping it in place. He rested one of his hands on Sans’s once again and gave it a gentle squeeze.

So … it’s okay. I know it’s not fun, and I know it … makes you upset, but … it’ll be over soon. Then things will go back to how they were before.”

Sans wasn’t sure when he had started shaking. Maybe he had been shaking before and he just hadn’t noticed it. He grit his teeth so hard he could feel them grinding even though they had never separated, even though he couldn’t _imagine_ them separated. It took all he had not to squeeze his hand into a fist while Papyrus was still holding it.

“How can you say that?” he bit out, turning away so he wouldn’t have to look at Papyrus’s wide, innocent eyes. “How can you look at it … how can you think …”

He felt Papyrus’s thumb rub against the back of his own hand, so gentle, so assuring, even though Sans could feel him shaking, too.

“He’s still our dad,” he replied, and Sans could hear the tremor in his voice, the uncertainty he forced away, the affection for the same man who had strapped him down to a table and sliced into his soul. “he … he still lov—”

“That’s not our dad!”

Papyrus stiffened. Sans winced, cursed himself several times over, but all he could make his body do was sit there, shaking his head, lifting his hands to dug his fingers into his skull.

“He can’t … whatever happened to him, that’s not … our dad wouldn’t hurt us,” he went on, his voice more absolute by the second. “He’d _never_ hurt us. Whatever happened to him, that’s not how he’s supposed to be, Pap, he’s supposed to … he’s supposed to take care of us, he’s never supposed to hurt us, _ever,_ no matter what.”

Papyrus didn’t speak for a few seconds. He lay there, staring back at Sans, so silent Sans almost couldn’t believe this was really his brother. His eyes drifted down to his hands, thoughtful, looking far more like Sans had been when he was in the middle of a difficult project and just couldn’t figure it out.

“I think he … he thinks he’s taking care of us,” he said, very quietly. His hands clasped together, his fingers fidgeting, his mouth pressed into a tight line. Sans could see his bones trembling, he had _never_ trembled before, he was so confident, so sure of himself, it had only been a few weeks and now he looked like a scared kid, and all Sans could do was sit there and make him cereal and tuck him in bed as if that would change a single damn thing once they got up tomorrow morning—“He … he _is_ taking care of us, he just … he’s worried about us, whether we’ll ever get to … see the surface, he’s worried we’ll get hurt down here, he’s—”

“ _He’s a fucking liar, Pap_! ”

Silence.

Sans didn’t even realize what had come out of his mouth until he saw Papyrus’s eyes widen, even more than before. Until he heard the words echo back into his own skull. And by then he was already panting, he had already yanked his hands out of Papyrus’s grip and squeezed them around himself, hugging himself as if, if he squeezed hard enough, he might be able to get away from what was all around him.

What was right in front of him.

His breath trembled, and his head shook back and forth as his smile spread shaky and tight.

“He … he shouldn’t … it doesn’t matter what he says, he … there’s something wrong with him, and … it can get better, this isn’t what he really …” He bit back another whimper in the back of his throat. “He’s just …”

Nothing else came out. Sans searched for the words, but nothing came. He just sat there, trembling, wishing that he could curl up just a little tighter and disappear completely. Maybe then he would stop hearing his own words fly back at him. Maybe then he would stop seeing Papyrus stare at him with too many emotions swirling in his sockets for Sans to read.

He had never sworn around Papyrus. Never. Something just seemed … wrong with it. Papyrus had never sworn. Sans was sure he had _heard_ curse words … probably … at some point … did anyone ever curse around Papyrus? Or did they just have the same sense that he did? That there was something too innocent about him?

Was Papyrus really as innocent as Sans had always assumed, if he could suffer through torture and still insist that the person hurting him meant well?

Did that make him even more innocent than before?

Papyrus wasn’t younger than him. Sans knew that. He knew there was no reason for him to feel like he needed to shield him from the world.

Especially since he hadn’t managed to shield him from what ended up hurting him most.

He stared at the floor, stared at his hands in his lap, stared at his feet—still wearing shoes, Papyrus hated when he wore his shoes on his nice clean floor. He hadn’t said anything about it. Sans wasn’t sure if he had even noticed.

When was the last time he had even had the energy to clean?

He listened to the soft sounds of Papyrus shifting in his bed. Despite his silence, he never seemed to stay still for more than thirty seconds at a time. He used to be so good at that. He could win at hide-and-seek when they were kids while standing in plain sight, just by being completely still. When had that changed? How much had Sans missed, because he hadn’t been paying attention?

“I’m sorry I lied to you, Sans.”

Sans clenched his hands around the fabric of his pants and forced his breath out in a trembling sigh. He couldn’t bring himself to look up and see the pained frown on his brother’s face.

“you don't have to be sorry, papyrus,” he murmured, as sincerely as he could. “i was lying to you plenty before that.”

Papyrus didn’t say anything for a minute, and Sans relaxed his hands as much as he could, stretching out his fingers even though they curled right back up a second later.

“It’s not good to lie,” Papyrus said at last, though there was no accusation in his tone. “Especially to people you love.”

Sans’s smile tightened, but he didn’t reply. Papyrus shifted a little more, and one of his hands reached out to rest on Sans’s own.

“I love you, Sans.”

Sans’s soul hurt. It hurt so much that he thought he was on the table again, being sliced open and ripped apart. But then he could at least close his eyes, and now, as hard as he tried, he found his gaze drifting up to meet his brother’s, to see those gentle sockets boring into his own.

“I think that’s why I lied to you,” Papyrus went on, so sad, he should _never_ sound so sad. “Because I didn’t want you to get hurt.”

It was hard to breathe. He didn’t even need to breathe, but for a second, Sans felt like he was choking. Papyrus tilted his head.

“That’s why you lied to me, too, isn’t it?” he asked. Sans didn’t reply. He didn’t know what he would have said if he could have forced a single word past his throat. Papyrus just tilted his head the other way and looked down at his hands. “I don’t think it helps. Lying just makes things worse. When you love someone … you should tell them the truth. Then they’ll tell you the truth, and you can help each other.”

He had never been mad. Even when Sans had lied to him, even when Sans had kept everything important from him, he had never been mad.

What right had Sans had to be angry, even for a second, when Papyrus had lied to him, too?

Wasn’t that what he had done before? For his brother and his dad? He had told them the truth, at least most of the time, because that was important. Because they _deserved_ to know the truth, at about the things that mattered, because he had never had a reason to lie to them, but now he _did_ and he _had_ and now that he had started, it was like there was no going back.

He had lied to Papyrus about the experiments. He had lied to his dad—or avoided telling him the truth, and wasn’t that the same thing? Then his dad had lied to him and he had kept all the work he was doing a secret and now …

Now …

If they had never started lying in the first place, would any of this have happened?

Papyrus’s gaze had shifted down again, toward his hands, and Sans could see his eyesockets beginning to droop. He always was an “early to bed” type of person, and that was when he had had energy to spare. Even when they were little, half the time Sans would sneak out of bed after Papyrus had fallen asleep to read by a flashlight or finish something he had started earlier. And when Papyrus wondered why he was so tired the next morning when he had to get up for school, Sans would just brush it off, insisting that yes, he had gone to bed at the same time Papyrus had, he just hadn’t slept as well, because he was afraid that if he told the truth, Papyrus would find a way to keep him from getting up and working on the things he enjoyed.

Had that been lying?

Was it easier to lie about the big things when he had lied about the small things for so long?

After several minutes of silence, Sans cleared his throat, and it felt like shattering glass.

“Hey, uh … you want me to read you something before you go to sleep?”

Papyrus lifted his head. “Like a bedtime story?”

“yeah,” Sans breathed, struggling to get out the sound.

Papyrus’s browbone furrowed.

“I thought we were too old for bedtime stories.”

“You’re never too old for bedtime stories,” Sans replied, so quickly that it felt like he had known it all along. As if it should have been obvious. He smiled a little wider, and it didn’t hurt quite as bad as he had expected. “‘specially not if you’re as great as you are.”

And there it was. That spark. That beautiful little gleam in his sockets, the glisten that made it _so easy_ to forget the faded marks on Papyrus’s bones, the weakness of his soul, every damn thing he had suffered through every damn day for who knows how long before Sans found out.

“Am I great?” Papyrus asked, sounding so much like his younger self that for a second, Sans could imagine that he was still the babybones who cuddled against his side as they both fell asleep.

Sans huffed a pained laugh. He smiled, and it had never hurt more to feel his mouth curl into his cheekbones. Still, his eyes softened, staring down at the most precious person in his world.

“The greatest.”

Papyrus smiled back, shaky and hesitant, but a bit more sure of himself, even if Sans could still make out the faint doubt in the backs of his sockets.

“Will you read one of the books from when we were little?”

“Anything you want, bro,” Sans said, without missing a beat, already pushing himself off the edge of the bed and getting ready to go hunt it down. He waited for Papyrus to give him a suggestion, but Papyrus just watched him, waiting, expectant. Sans fidgeted and wracked his tired mind. “How about _Fluffy Bunny_? You always liked that one. ”

There was just enough of a spark in Papyrus’s eyes to make Sans’s shoulders relax and his smile tilt into something a little more genuine as his brother gave a small nod. “Okay.”

Sans nodded back, and slipped out of the room without another word.

It took him ten minutes to dig through the boxes in the attic and find their old collection of children’s books, but at last, he found it, in the back, by the wall, covered in dust so thick he almost thought it had snowed. For once, he was grateful of his dad’s packrat tendencies. Once the box was open, he found the _Fluffy Bunny_ series right at the top, and after a brief moment of debate, he picked up the whole stack and carried them back down to Papyrus’s room.

Papyrus’s face lit up as soon as he saw the cover, just as it had all those years ago. He settled further under the covers, and Sans pulled up a chair close to the bed, dimmed the lights, then sat down and opened the book.

He had never read Fluffy Bunny before. It had always been their dad, or Alphys, or Mrs. Drenton, or one of the other babysitters. Sans had listened to thousands of bedtime stories, but he had never told one. He didn’t even know if he was any good.

Papyrus never complained.

His eyes were half-shut by the time he had made it through ten pages, and by the time the book was complete, he had cuddled up against the mattress, his sockets closed and his face smoothed out, all his worries forgotten.

Sans set the book aside, but he didn’t leave the chair. He sat there and looked at his brother. The person he had lied to. The person who had stepped up when he had stepped back. The person who had only ever wanted to protect him, even when he was small. The person who found a way to love even when those he loved hurt him.

Betrayed him.

He would have understood why Sans wanted to stay up and read. He would have found a solution, if Sans had just told him.

He would have found a solution to all of this, even if he couldn’t fully understand it.

He would have found a way to make everything work out.

But they never gave him the chance.

Sans reached out and brushed his hand over his brother’s browbone, watching his smile tilt up at the gentle caress.

“I’ll fix this,” he whispered, barely louder than a breath. “I promise.”

Papyrus slept.


	27. Chapter 22

Sans fell asleep in his chair beside Papyrus’s bed that first night, half an hour after he put the book aside. After the third night, he woke up to find himself tucked into bed next to his brother.

On the fifth night, Papyrus just patted the bed beside him, and Sans climbed in without a word.

He didn’t go in his own room anymore, except to grab clothes to change every couple of days—on Papyrus’s insistence that “even if he didn’t leave the house, he still needed to look presentable.” He didn’t even notice whether or not his bed was made. Funny how that had seemed so important a few weeks ago. How many weeks had it been? It had only been two, hadn’t it? Two weeks since he had found Papyrus in his dad’s lab. Two weeks since he had realized exactly how much everything had gone to shit.

He had counted the days at first, but after a while, he lost track, and he didn’t see the point in trying to get back on track. There was nothing to mark the passage of time if he didn’t turn on his computer, and he had done everything on paper, tucking it safely away to avoid being seen, just in case his dad decided to snoop—even though he never had before. It was easier, in a way, not knowing how long it had been.

It made him feel just a little less like he was running out of time.

This morning was no different than any other. He woke up next to Papyrus, his head tucked under his chin, his arms tight around him. Papyrus had been awake for a while, as usual, and gave him a smile Sans could almost believe was real.

They laid there until their dad called them out. He had noticed them sharing a bed, but aside from a slightly pained look, he had said nothing about it. Papyrus still ate breakfast at the table, with their dad, while Sans just sat there, waiting, watching. He never had any appetite in the morning anymore.

Papyrus and their dad finished eating. Their dad washed the dishes and set them out to dry. Then he started toward the door, Papyrus trailing close behind him, and Sans stared at the floor, bracing himself for one more day on his own.

“You can go out today, if you’d like.”

Sans’s head jerked up so fast his neck hurt, but he ignored it, his attention focused entirely on his dad.

His dad wasn’t looking at him. He was staring at the door, though Papyrus, at his side, looked between them both with wide, curious eyes, still silent. He was silent so much of the time nowadays. Sans wasn’t even sure if he had spoken a word around both of them for the past two weeks.

But he hadn’t heard wrong. Sans had no doubt about that. Everything he knew about his dad might have been wrong, but he could read the tense line of his shoulders as well as ever.

And when his dad glanced over his shoulder a few seconds later, Sans had all the confirmation he needed.

“I think I can trust you with this, can’t I?” his dad asked, and his voice was so pleading it made Sans want to strangle him all over again. Sans didn’t respond. His dad sighed and looked at him with soft, almost begging eyes. “I don’t want to do this, Sans. Please understand. I want what’s best for both of you. I want you to have … everything I’d hoped you could.”

Sans said nothing. His dad waited, as if Sans might suddenly change his mind and speak. But he was far too smart to actually believe that, and after ten seconds, he looked away again.

“But I suppose there’s no good trying to convince you of that now, is there?”

Silence. Papyrus shifted from foot to foot and wrung his hands. For the first time, Sans wondered whether it would have been a good idea to tell Papyrus what he was doing, or whether it was better not to risk the slightest chance of it getting out, at the cost of his brother thinking he was just going to let him suffer in silence.

His dad sighed one more time and put a hand on the doorknob.

“Please don’t do anything you’ll regret. I can’t let this project fail, Sans. And if you do anything that would jeopardize it …”

He trailed off then. Sans waited for the threat, but none came. His dad just looked at him, his eyes sad, yet just as serious as they had been every day for the past two weeks. At last, he sighed.

“Please, don’t,” he finished, with the tone of someone being pushed into doing something he hated. “I don’t want to keep you locked up here, but I will if I have to.”

He didn’t wait for Sans to respond this time. He turned the doorknob and opened the door, stepping inside. Papyrus spared Sans one more unreadable glance before he followed close behind him.

And Sans was alone.

For ten minutes, he stood there, looking at the door, as if afraid that his dad would be waiting on the other side of it, ready to catch him if he tried to leave. He had said he could leave, and he must have guessed he might go to his lab. That was what he wanted him to do, wasn’t it? Go back to how things had been before he had been found out? So wouldn’t he be doing exactly what his dad wanted?

But even when he finally dared to step up to the door, he took more than a minute to edge it open, and another minute to scan the surroundings to make sure his dad wasn’t there to see him.

Then, when he was finally as satisfied as he was going to get, he closed the door, ran back up the stairs, grabbed an empty bag from his overstuffed closet, and ran around the house, shoving in everything that struck even the slightest sense of being useful.

The most important thing was already at the lab, of course, and he didn’t really know all he would need. But he didn’t want to have to make any return trips today if he could avoid it.

Less time wasted meant less time Papyrus had to suffer.

He poked his head out the door one more time, a bit less hesitant than before, before he stepped onto the porch, closed the door behind him, and broke into a run.

The lab was further away than he remembered. Maybe because he had always been so happy to go there before. He had been excited, but not desperate. He didn’t mind stopping to chat with monsters he passed on the way, even if he picked up his pace a little afterward. Now, even though several people tried to talk to him on his way, he never paused.

He was probably worrying them. They hadn’t seen him in two weeks, after all. Sure, he had been a little reclusive before, holed away in his lab half the time, but it had never been this bad.

He didn’t pause to see their faces after he passed them.

Later. When this was all over.

Would it even matter, once this was all over?

It took him three tries to unlock the door to his lab once he reached it, and he almost dropped his bag slipping inside and slamming the door shut.

He didn’t realize he was shaking until he crossed the room and flopped down in the chair at his desk.

He looked around the lab, taking it all in. Had it really only been two weeks since he had been here? There was no visible dust, nothing changed, nothing moved. Of course there wasn’t. Only he had the key, and he hadn’t been here. Two weeks. Had this all really seemed so important just two weeks ago?

His eyes fell on the T.F. machine, pristine, refurbished, and well-used.

That was his pride and joy. Maybe he hadn’t built it, but he had used it. He and Alphys had figured out a mystery that had left even Dr. Billington stumped. They had discovered something revolutionary. They were going to change the world.

They were going to get everyone out.

That had seemed so important before, hadn’t it?

And if he went through with this …

Sans clenched his teeth and looked around the room, at every tool, every machine, the sparse set-up he had made for himself.

It wasn’t much to work with, and he didn’t dare get any other supplies from the main lab. And it would mean dismantling parts of the machine he had admired for so long from a distance, the machine that had inspired his thesis, the machine that had been the focus of nearly all his attention since he first began working at the lab.

But it was all he had. And it would be enough.

It had to be.

He began emptying the contents of the bag at his side, spreading them out on the desk so he could have all his asserts visible, so he could figure out where to start and where he was trying to go. He would have to salvage parts from the garbage dump, for sure, and he would probably have to buy at least a few things. He still got his paychecks delivered in the mail every two weeks, and as his dad was still paying for their house and essentials, he had plenty of gold to spare. He had most of his tools here from the work he had been doing before, so that was taken care of. There were several other things in their house he probably could have used, but he wasn’t going to risk taking anything his dad might notice was missing, and he could work with what he had picked already.

Only after he had inventoried everything else did he notice what he had left at the bottom of the bag.

It was fairly large, larger than most of the other things he had packed, and it was a miracle it hadn’t been squashed underneath everything he dumped on top of it. He hadn’t been thinking when he threw it in, no more than he had been thinking about the rest of the things he had dumped in on the off chance he would be able to use them.

But as he pulled it out and held it in both hands, he couldn’t bring himself to put it back.

Papyrus had a lot of different hobbies. Or, he _had_ had a lot of hobbies, before their dad had dragged him into all of this. He had never much cared for the stuff they studied in school, and college had never interested him, but that didn’t mean he didn’t love to learn. Every now and then he would take up a new activity and become as skilled in it as he possibly could—which sometimes was about the level of a five-year-old and sometimes was just as advanced as a professional.

And one of his absolute favorite hobbies was scrapbooking.

For a good two years, every one of the gifts he gave out for birthdays or holidays—or for no reason at all—was a scrapbook. A scrapbook of magazine clippings, flat mementos, and, more than anything else, photos. Around the same time, Papyrus had gotten a camera for his own birthday, and had taken to snapping as many pictures as he could of just about everything around him. It had been a little annoying at times, finding a camera in his face without any warning, taking photos of the most awkward, random moments, but Sans could never stay irritated when Papyrus got the photos printed and smiled so wide while looking through every one.

It never failed to amaze Sans that his brother knew exactly which photos would work best in a scrapbook for any given person. No matter who it was or what the occasion, Papyrus could throw together a full-sized scrapbook in no less than two days, and make it look like he had spent two months putting it together.

Their dad had received six in total, and seven for Sans, but only because Sans and Papyrus’s shared birthday fell near the beginning and the end of what Sans called “the scrapbook streak.” Sans kept all of his on his bookshelf, near the wall, so he could get to them right away if he ever felt like looking through them.

It must have been six months since he had last pulled one off the shelf, yet there it was, thrown in there with the rest of the things Sans’s frenzied mind had apparently deemed important.

The last scrapbook Papyrus had made for him, on their eighteenth birthday.

There was nothing all that special about it, really. Nothing that made it any more special than the other scrapbooks Papyrus had made, except for the fact that it had been the last one. Sans had looked through it several times before putting it up on his bookshelf, laughing at the embarrassing shots of him as a baby and toddler, the awkward picture his dad had taken on his first day of college, photos of him hanging out at the lab with his dad’s co-workers, and copies of pictures taken on every one of his and Papyrus’s shared birthdays for seventeen years prior.

It had been special before, but the sort of “special” you called things you knew were meaningful, but never spent that much time appreciating until much, much later.

He hadn’t thought “later” would be this soon.

Despite the voice in the back of his mind telling him that he didn’t have time to waste, he opened the cover and flipped through it again. Papyrus had arranged all the pictures in chronological order, and it was like taking a walk through his own life. A life he had almost forgotten existed.

Had they all really smiled that much? Had things really been so … easy?

They hadn’t, of course. No one took pictures of the bad times.

But had the bad times really been that bad? He had barely thought of them before. Sometimes they were long, but they were never hard, his dad had made sure of that. Even when he could barely spend time with them for how much work he had to do, he always made sure there was someone there to take care of them, he always made sure to spend at least a _little_ time with them himself.

And he was never mean. No matter how bad things got. No matter how stressed he was.

It could have been better.

But it could have been worse.

He would have taken twenty more years of those bad times over another two weeks of these.

He flipped through the pages and found himself smiling, chuckling, even as the backs of his sockets burned with tears he never shed. Half the photos of him had Papyrus in them as well, and he paused at every shot, running the tips of his fingers over those bright eyes, that wide smile. He tried to engrave it deep in his head, so that no matter how far-away it seemed, he never forgot it.

He could never forget it.

That was what he had to get back.

His chest sunk as he neared the end of the book, finishing up the photos of him and Papyrus as goofy seventeen-year-olds. He flipped the pages a little slower, trying to make it last, as if he could spend just a little more time in that world. It wasn’t so hard to imagine. They looked almost exactly the same as they did now.

The smile Papyrus had worn then was the same one he should be wearing now.

Sans swallowed as he turned the last page, with one more photo on the left and the blank inside cover on the right.

And …

His browbone furrowed as his eyes settled on the piece of old, folded construction paper tucked against the back cover, before it rose again and he let out a long, shaky breath.

… right. He had forgotten about the card.

His dad had kept it in a frame in his bedroom for a good ten years after he and Papyrus had made it for him. Even though he was about the worst housekeeper that had ever been born, he always made sure that that frame was properly dusted, carefully maintained, treasured as much as the card inside it.

Sans still didn’t know how it had fallen off the wall. None of them did. They had gone out one Saturday, almost a year ago now, and when they came back, the frame had fallen from the wall, shattering on the ground and leaving the card in the middle of the mess.

His dad had been distraught, but Sans just laughed and pulled the card from the wreckage, insisting that they could get a new frame and hang it up again, just like before.

He had forgotten that he slipped the card inside the scrapbook for safekeeping.

None of them had remembered to buy a new frame.

It didn’t make any difference. Maybe his dad had missed it, and maybe he hadn’t. They still had every other picture in the house. They still had each other. Nothing changed.

And the card remained in the back of the photo album, tucked away, waiting to be found.

Sans looked down at it, picking it up as gently as his trembling fingers could manage. Three faces smiled up at him. God, he had sucked at drawing back then. Even for stick figures, they were awful. The heads weren’t the right shape and everyone’s arms were too long and the only thing that even identified each person were the clothes they were wearing. And his dad’s bad eye, of course.

It shouldn’t have been this weird, to see his dad smiling, and to believe it. He had seen it so many times before. He had seen it in photos all around the house.

But _he_ had made this. This had been what he had seen, at eight years old, what he had put down on paper, even if he hadn’t been skilled enough to accurately represent it. This had been his dad.

And looking at this picture now, it was so easy to remember him, just as he had been for the first nineteen years of his life—even if the past two weeks had made it seem like a world away. It was so easy to remember the gentle smiles, the hugs, the bedtime stories, the cuddles, the soft words, the encouragement and the way he tried so hard, even if he failed, he always _tried_ to make them happy.

Sans’s fingers tightened around the edges of the card. He laid it down on top of the album and dug around in the closest drawer until he found a pen. His hand trembled, and he spent a half minute just staring before he forced himself to uncap it and bring it down to the edge of the page.

The two words flowed out before they even had the chance to reach his head, his own natural font outweighed by the shaking of his fingers.

_don’t forget._

His eyes shifted back to the drawing, to the three smiling faces, his brother, his _dad._ Very carefully, he slipped it into the back of the photo album, closed it, and placed it inside a drawer in the small desk by the wall.

That was still him, deep down. He was still in there, somewhere. And Sans would bring him back. Even if he had to go back in time and find the man he used to be. Even if he couldn’t see him anymore. He was still there. And as long as Sans remembered him, as long as Sans remembered what he was fighting to regain, he could still fix this.

He would get their dad back. Their _real_ dad.

One way or another.

He turned back to the machine, took a deep breath, and got to work.


	28. Chapter 23

**Notes for the Chapter:**

> Just so you all know, I'll be going on a short hiatus starting today - I'm having a very minor surgery and two wisdom teeth out over the next week, plus I have an exam, my grandmother's wedding, and need to finish revising my current original novel. So ... tad busy. XD Anyway, I'll be gone until the middle of next week - the next chapter will be posted on Thursday, October 5th. As always, thanks so much for your support and feedback, and I'll see you guys then!
> 
> Oh, and just a quick reminder: even though Sans may partially blame himself for this whole mess in-story, the author does not.

The calendar said it had been a month, but Sans had never doubted traditional measurements of time more in his life.

The calendar didn’t measure how long it felt. The calendar didn’t measure the way the days dragged on, how far away the “old days” seemed to be. The calendar didn’t measure how Papyrus’s smile grew a little shakier with each day that went by, how he seemed so much better in the mornings even if he could barely stay on his feet some evenings. The calendar didn’t measure the important things, and Sans didn’t like to look at it.

He didn’t like to be reminded how long it was taking him to make any progress at all.

Sometimes he found himself pausing in the middle of his work and just staring at the machine, fighting back the impulse to bang his head against it—or maybe to tear it apart and run back home and find some other way out of this. He felt stupid. He felt selfish. He had decided this was the right thing to do, but he didn’t _know_ that it was the right thing to do, and it didn’t stop his brother from suffering, his brother didn’t even know that Sans was trying to find a way out of this.

As far as his brother knew, Sans had given up, and was resigned to simply caring for him every time he came back from a day of experiments.

But he still had a smile for him. Shaky and weak and afraid, but still, a smile.

Never did Sans get even the smallest impression that Papyrus was angry with him for not keeping him safe.

And it made Sans hate himself even more.

Papyrus didn’t ask for bedtime stories, but Sans still read them. Every night, whether it had been a “good” day—or whatever passed as a good day now—or one of the worst. Usually one of the _Fluffy Bunny_ books out of the box in their attic, but occasionally a book on puzzles and, once, one of Sans’s old physics textbooks, though Papyrus told him after that that he preferred not to be bored to sleep.

The stories never put him to sleep, though. They calmed him down, they soothed him, but his eyes were always open, if drooping, by the time Sans closed the book.

Papyrus wouldn’t sleep until Sans had put the book away, kicked off his shoes, and slid into his brother’s bed beside him. Without a word, they wrapped their arms around each other and snuggled close, as close as they could get, Sans tucking his head under Papyrus’s chin and stroking the side and back of his skull as Papyrus ran gentle fingers up and down Sans’s spine.

Sometimes, Sans could pretend they were babybones again, comforting one another after a bad dream.

But if they had really been babybones, they would have been climbing into their dad’s bed, snuggling into his sides while their hands clasped together on top of his chest.

And Sans didn’t like to think about that for very long.

He hated mornings. He hated opening his eyes and not knowing what time it was and not daring to look at the clock for fear that he would find only a few minutes left until it was time for Papyrus to leave. Even if he found that he had woken up hours early, he never went back to sleep. He stayed and stared at his brother, memorizing every feature, cherishing every breath he took, holding him tight and biting back the tears that burned his sockets.

He made sure the tears were gone by the time Papyrus woke up.

Gaster woke them up, but didn’t eat breakfast with them. He tried, sometimes. Or he had at first. Maybe it had been his way of convincing himself that they were still a family. That things weren’t all that different. If Gaster offered to eat a meal together, Papyrus always agreed, and Sans could never bring himself to say no if Papyrus asked him to join them.

But that didn’t stop the awkwardness, the tension so thick Sans could have built another house out of it.

Gaster didn’t try to eat breakfast with them after the first week.

They ate, separately, and Gaster only interacted with them when it was time to take Papyrus away.

Sometimes, he didn’t take Papyrus in the mornings. Sometimes he would tell Papyrus to meet him in the lab that evening instead. At first, Sans had been relieved. At least until his brother came home after that first “evening session” ready to collapse from exhaustion and pain, and Sans had realized that Gaster wouldn’t dare do any experiments bad enough to make Papyrus scream when there was anyone else in the lab.

And on the evenings—and the weekends—he was alone.

Sans found himself battling, every morning, between the wish that Gaster would never tell them it was time to go, and the desperate hope that he wouldn’t leave without Papyrus at his side.

He didn’t even try to convince Papyrus not to go when he was called.

He always went, without any coercion, any reminders. Without Gaster even coming back to get him.

It made Sans want to give up on the machine and just break Gaster’s neck.

Most mornings, though, Gaster took Papyrus with him, and Sans couldn’t decide, even now, whether that was a form of mercy.

Sans hugged his brother before he left, always, no matter how much it hurt, no matter how much he hated feeling his da—Gaster’s eyes on him, watching him with that soft look that _wasn’t real,_ because it _couldn’t_ be real, no one could look at him like that and still do what he did. No one could mean it.

No one else could look so much like his dad had.

Papyrus squeezed him, murmuring reassurances that everything would be alright, reassurances Sans should have been giving him instead. Reassurances he could rarely get past his tight throat.

He watched through the window as they left. He watched, and he waved when Papyrus turned around to flash him a quick smile. It was like lifting his hand with a half-ton weight strapped to his wrist.

And as soon as Gaster and Papyrus were gone from view, Sans slipped out of the house and started on his way toward Waterfall, toward his lab, toward the machine that took up every bit of time he could manage away from home.

He didn’t go to the main lab anymore. He didn’t need anything from it—nothing he couldn’t pick up at the garbage dump or a shop, anyway—and, more than anything, he didn’t want to go back there if he didn’t have to. It would only make things worse. It would only remind him how bad things had gotten, and how helpless he was to do a damn thing about it.

Maybe that was selfish, too.

He had never asked Papyrus whether he would have felt better if his brother was there during the experiments. He tried not to think about it. He tried not to consider whether his brother would have been happier if he had forgotten all about the lab and just stood nearby and held his hand through all the pain.

He tried to convince himself that what he was doing was best.

But then again, that was what Gaster was trying to convince himself of, too.

At first, he was careful. At first, he would spend a few hours at the lab, then come home, just in case Gaster decided to end their “session” early. But he found himself spending a lot of time just pacing around the house, thinking about what Papyrus was suffering through at any given moment. And even if Papyrus came back earlier than expected, Gaster rarely did. So Sans stopped being quite so cautious. He waited for it to bite him in the backside, waited for the reminder that even the slightest slip-up could mean his whole plan being ruined. It never came.

Gaster never asked him where he went during the day. On a couple of occasions, Sans had even come back after Gaster and Papyrus had gotten back to the house, and Gaster hadn’t said a thing about it.

It was … confusing. And a little bit worrisome.

But then again, Gaster had trusted him enough to give him free reign during the day. He had known he would be leaving the house. Maybe this was another one of his attempts to seem like he meant well.

And Sans wasn’t about to bring it up and risk losing the freedom he had gained.

So he left in the mornings, and came back in the evenings, and he tried very hard not to think about Papyrus—or Gaster—while he was in the lab. He immersed himself in his research, in his work, only leaving when he needed to gather new parts from the dump. At first, it was easy. Scrap metal was fairly common around here, and given that he already had the entire T.F. machine to work from, he was hardly in want for materials. But as he delved deeper into the project, as he realized all the little pieces he hadn’t anticipated needing, he found himself spending more and more time just searching for the right parts to continue with the machine’s construction.

On top of that, there were plenty of tasks he wasn’t nearly experienced enough with to complete in a reasonable amount of time. He was good at engineering, sure, but it wasn’t the focus of his studies, and while he could _understand_ computer code, he was a long way from being able to write anything particularly advanced. He tried, initially, to just pick up what he needed from borrowed books or trial and error, but he soon found that going that way would likely triple the amount of time needed to finish this project. He couldn’t put Papyrus through this any longer than necessary. To get this done quickly, he would need help. And even once he _got_ that help, that didn’t take into account the fact that he had no idea if any of this was really going to work.

But even when he felt the weight of all of this crushing him, even when he found his head spinning with the realization that he had _no idea what he was doing, it was impossible, it was a bunch of science fiction crap, he was never going to help his brother he was just wasting time he was—_

He never stopped. He never gave in.

He couldn’t give in.

He wasn’t ready to consider the alternatives should he give up on this one chance.

The calendar said it had been a month, and if Sans looked at the machine now and tried to remember what it had looked like when he had started, he could almost convince himself that this wasn’t just a waste of time. What stood before him now was almost unrecognizable as the T.F. machine. It was a good deal larger, for one. The panel that displayed readings was still there—he wasn’t willing to get rid of everything Dr. Billington had spent so long on—as well as some of the original control panel, though quite a few more buttons had been added, and he had gutted out quite a bit of the wiring. Even more notably, there was now a large space inside hollowed out for someone to stand in if the machine itself actually managed to send them back through time. It was … silly, but a tiny part of him that had never aged past eight years old couldn’t help but beam at the thought that he was actually _building_ one of the fictional contraptions he had read about. He couldn’t help but picture himself standing inside it, zooming through spacetime, typing in coordinates and visiting any times or places he could imagine.

Then he remembered why he was doing this in the first place, and his excitement snuffed itself out.

Besides, it wouldn’t work that way, he knew, even if it succeeded. At the very best, he would be able to travel back along the time stream and end up in a place _relatively_ close to the one he was aiming for. He still hadn’t figured out how he was going to get back, or if he would or _could_ go back, once things were changed. Traveling backward and forward in time were two completely different things, and if he made a significant change, would he even be able to go back to the altered future?

If he stayed … did that mean he would have to kill his other self to avoid a paradox?

Or maybe just die and let his younger self take over and hope he made better choices this time around?

There were increasingly more moments when that sounded like the best choice.

Then again … if his younger self couldn’t really understand how badly things would turn out if he stuck to his ways, if he pushed his dad into making the choices that had started this whole mess … maybe it would be better to stay there himself.

He tried to shake off those thoughts for now. They weren’t helping anything. Unless he could actually get this machine working and send himself back far enough in time, it wouldn’t even matter.

He kept his eyes on his work as he pulled his phone out of his pocket, a couple hours after he had arrived at the lab. His fingers moved over the keypad on reflex, typing in the number he really should remember to put on speed dial one of these days. It rang once, twice, before he heard a faint click on the other end of the line, and a small, muffled yawn, as if the person on the other end had only just woken up.

“H-hello?”

“Hey, Alphys,” Sans said, trying to put a bit of a smile into his voice even though he couldn’t manage more than his automatic grin on his face.

He could hear Alphys perk up a bit on the other end of the line.

“Oh, h-hey, Sans. H-how are you?”

“Did you get the data I sent you?” he asked, as if she hadn’t said anything.

She paused, and he could almost see the furrow in her brow, the concerned purse of her lips, though of course, she said nothing about it.

“Um … y-yeah,” she replied at last. “I t-took a look at it. I’m n-not really sure what you’re trying to d-do with it, you didn’t s-say—”

“I need a program,” he cut her off. “Something that can create a virtual map of the knowledge of the timelines we have now. As far forward and back in the timeline as we can go.”

More silence. Sans could hear her shifting around wherever she was standing—probably in her room, judging by the amount of clutter she seemed to be stepping on.

“Uh … s-sure. I mean, I can t-try. I’ve n-never tried to make anything that l-looked at another point in _t-time,_ but …”

She trailed off. At first, he thought she might be doubting her abilities again, and he tried to remember what he used to say to make her feel better, to make her believe that she _could_ do it, even though those old days felt like a world away. But before he could speak, she cleared her throat and shifted around some more, her foot bumping up against what sounded like an empty soda can.

“W-what are you working on?”

Sans looked at the machine. It barely resembled what Alphys was used to now. This whole _lab_ barely resembled what she would remember from the last time she had visited. He wasn’t even sure if _he_ would resemble the Sans she remembered.

He could hardly remember what that Sans had been like in the first place.

He let out a small, heavy breath.

“just … more timeline research.”

“A-anything in particular?” she asked, her voice even more hesitant than before.

“No,” Sans said, swallowing back all the words that tried to force their way up his throat. “Just … just the stuff we were working on before.”

Another pause. Sans could hear her fidgeting.

“Do you w-want me to come and s-see? I m-might be able to help, if I could s-see it in p-person—”

“No,” he cut her off. She went silent. Sans stiffened, listening to his own words echo in his head, before he sighed. “No, it’s … it’s fine. No reason for you to come all the way over here just for that.”

Alphys didn’t say anything. Sans turned his attention back to the machine, looking over internal circuits he was still trying to get connected. He really wasn’t a hardware person. Sure, he could _understand_ these machines, but he rarely _built_ them. And he had never had to search for supplies to make them before.

He needed her help. For far more than the software, really. She had always been better with technology than he was. She could make this go twice as fast as it was already if she was actually here to see it.

But Alphys wasn’t stupid. Once she saw what he was doing, she would know that something was up.

“S-Sans … are you okay?”

Or maybe she already did.

Sans bit back a curse. He was sure he didn’t actually make any sound, but he could already hear Alphys stuttering out an explanation, as if she wasn’t allowed to just be worried about her friend without several dozen valid reasons.

“I m-mean, I never s-see you anymore … if it’s something I did—”

“No, no, you didn’t do anything,” he said, before she could even get the full thought out. Before it had a chance to solidify in her head more than it already was.

He had enough trouble making sure Papyrus didn’t blame himself for Sans’s decreasing HP, or his lower moods. He wasn’t going to have Alphys think that there was a damn thing she had done wrong when she had been one of the only rocks he could count on in the middle of this mess.

He wouldn’t have been able to do half the work he had already done on the machine without her help.

But calling her had been risky enough. If she saw him—and moreover, if she saw the _machine_ —she would put enough of the pieces together to reach some less-than-pleasant conclusions.

Alphys wasn’t stupid. She was the furthest from stupid Sans could imagine, she was _brilliant,_ and maybe she didn’t notice everything, maybe some things that should be completely obvious went right over her head, but in other ways, she saw everything. And disassembling the machine he had admired from the age of seven in order to build something he refused to explain …

… she wouldn’t accept any of the fake excuses he could come up with.

He stood there for a minute, phone against his skull, before he noticed that she hadn’t said anything. If he listened closely, he could still make out her breathing, but she hadn’t said a single word. He furrowed his browbone.

“You still there?”

Another few seconds passed, and he heard her shuffle before letting out a soft sigh.

“… yeah.”

Sans winced at the vague sadness in her tone, and closed his eyes before pressing the phone even more firmly to the side of his head, trying to smile, even though she wouldn’t see it.

“look, i … I’m sorry, Al,” he said, swallowing back the lump in his throat. “I know I’ve been … things have been … I’ve been really focused on this, but … it’ll get better soon. Once I’m finished with this, we can … go get ice cream together. Or something.”

She said nothing. He forced his smile a little wider.

“You can show me one of those TV shows you like.”

He could hear Alphys laugh, a breathy, humorless sound that came across as more concerned than anything. “You h-hate anime.”

“It’s not all bad,” he replied, searching his memory for one of the shows she had insisted he watch over the years, or even one that she had put on to entertain Papyrus when they were kids. “That one about the lady that gets turned into a robot was pretty cool.”

He didn’t need to see Alphys to hear her perk up, her eyes aglow with the enthusiasm that had only increased with age.

“Oh y-yeah! That’s one of my f-favorites. A-and I a-actually found another season of Sailor Moon l-last week, b-but it’s really far a-ahead in the show so there are a lot of gaps from the DVDs I’m missing but it’s really really good so far and you’ve gotta come over some time and watch it with me, Sans, you wouldn’t believe what happens, it’s—”

He found himself smiling even as her words faded into a blur, melded with all the other ramblings she had gone on since they had first met. It had been a little annoying once, especially in his early teens, when she wanted to watch anime during her visits and he just wanted to read his physics books. But he had always admired her, from the first time she stepped into their house fourteen years ago, anxious and unsure, even around a couple of five-year-olds, but had all but lit up when Papyrus asked her what she did for fun.

Even when none of his classmates had understood him, she always did. It didn’t matter that they weren’t exactly alike. It didn’t matter that she preferred technology and biology while he preferred physics. It didn’t matter that she adored anime with every ounce of her being and he found it tolerable at best.

She had always been there. She had always helped.

She had always listened.

Sans gripped the phone a little tighter, letting his eyes fall shut.

It would be so easy to tell her the truth. So easy to just _tell_ her what he came home to everyday, what Papyrus suffered through, _what their father was doing to him._ It would be so easy to ask for her help, and chances were, Gaster would never know. At least until he had to face the consequences for his actions.

But …

Even when he was a kid, even when she had first started babysitting him, she had always admired his dad. _Everyone_ admired his dad, but Alphys … he had been one of her idols since long before Sans met her. He was her goal, he was her role model, he was everything she had wanted so badly to be herself, even if she had never pursued it.

Would she believe that the man she admired so thoroughly was capable of … this?

Even if she did believe it …

Alphys wouldn’t approve of what Gaster was doing. Of course she wouldn’t. She was kind, she was sympathetic, she was the best friend he had ever had, but—

His dad had been kind and sympathetic, too.

Sans gritted his teeth. No. Alphys wouldn’t do that. She wouldn’t … just think it was okay, she wouldn’t brush it off, but—

But she wouldn’t do anything about it.

She would _want_ to, but … Alphys was many things, but brave wasn’t one of them. Would she have the guts to say something, to someone important, at the risk of permanently ruining the life of someone she admired so deeply?

Wasn’t that exactly what Sans didn’t want to do?

He finally noticed the pressure under his fingers, just in time to avoid snapping the phone in his grip. Even as Alphys continued to talk, he turned his attention back to the machine’s gutted inner wiring. He didn’t need to tell her. He didn’t need to tell anyone. He could fix this. He had made this mess, he had started this whole thing, and he _would_ fix it.

He would fix it, and his dad would go back to being his dad.

Papyrus wouldn’t hurt anymore.

If everything went well … he would never remember he had been hurt in the first place.

Even if another version of him would. Even if another version of him would continue to suffer. Even if there would always be another version of him that Sans abandoned in this universe just so he could create another one where he didn’t have to deal with his mistakes, even if—

Sans paused.

His eyelights narrowed, and he leaned in a little closer, peering into the inside of the machine. He blinked a few times to clear his eyes, to be sure that he wasn’t just seeing things after so long staring at this thing. But he wasn’t. As long as he looked, it never went away.

There was a new part.

It was small, almost imperceptible, hidden between two of the control boards, linking them together. That hadn’t been there before. Or … had it? It was so small, maybe he had missed it … but those control boards hadn’t even been there before, had they? They hadn’t been in that spot, at least. He could have sworn they had been in two other places in the machine, far away from each other, and they hadn’t been linked, and—

He couldn’t remember.

He couldn’t remember what the machine had looked like before.

It hadn’t been that long, had it? Was a month really that long, when he had spent _years_ studying the design of this machine, when he had spent all seven years of his higher education thinking about what he might do if he had access to it, when he had written his _thesis_ on spacetime readings, the very readings this machine had made possible?

Had he really mutilated it so much that he couldn’t even remember what one of his idols had designed?

Had he really changed something about it so casually that he had forgotten he did it?

“Sans?”

Sans jolted at Alphys’s voice and straightened, forgetting for a second that she was on the phone and not standing right in front of him.

“yeah?” he asked, his tone only slightly shaky, though a good deal quieter than it usually would have been.

Alphys paused for a long minute, and Sans tried to imagine her face. It had been so long since he had seen her face, but he could still picture her crooked glasses, her awkward, yet genuine smile, the gleam in her eyes when she discovered something new that sparked her interest.

The affection he had seen in every look since he was a kid, making him wonder whether this was what it felt like to have a big sister.

“You’re not really okay, are you?”

It was smooth, gentle, and sure, without even a hint of a stutter, and Sans found himself unable to speak. All he could do was stand there, squeezing the phone against the side of his skull, words growing and fading in his throat. After a minute of silence, he heard her sigh, the faint shuffle on the floor as she shifted her feet against the clutter around her.

“Please let me help,” she said, and he hated himself, he hated himself for doing this to her, to _Papyrus,_ for keeping this whole damn mess a secret even though he couldn’t imagine doing anything different. “I just … I’m worried about you, you and Papyrus and Dr. G-Gaster, I … I know I’m n-not the only p-person you spend t-time with, and m-maybe you’ve got more i-important things to do, but p-please just … I know something’s w-wrong, so p-please—”

“i gotta go, al,” he cut her off, his voice breaking as he forced the words out past his teeth. “talk to you later.”

“Sans—”

Sans pulled the phone away from his head and ended the call.

He stood there for at least five minutes, staring at the phone in his hand, before he finally threw it across the room, almost hard enough to hit the opposite wall. It bounced against the floor, cracking the case but leaving the phone apparently intact.

He would need to fix that. It wasn’t like new phones were easy to come by down here.

But …

What the hell did he use it for, other than to call Alphys? Who was the last person he even _talked_ to, other than his brother? Didn’t he talk to people before? Sure, he had never been the most social monster around, but at least he talked to a _few_ people.

At least he talked to his friends.

Alphys. Dr. Japer. Dr. Lemming. Dr. Frewth.

His dad.

What was there in his life anymore? How much had there been before that he didn’t even think of nowadays? How much had he lost, how much had he thrown away because he was _stupid_ enough to start this project in the first place? His dad—Ga—he had been the one to continue, but Sans was the one who insisted they do it. He had pushed, even when his dad had resisted. He had pushed him past his limits and now he was gone, he was lost, and Sans didn’t know if he would ever get him back and Papyrus was hurting because of him and he was lying to his best friend and this was _all his fault_ …

He squeezed his sockets shut, sucking in a deep, shuddering breath. His hands curled into fists before he forced them to relax again.

He crossed the room, picking up the cracked phone, and slipped it into his pocket. Then he turned to the machine. The butchered machine he had once idolized, the magnum opus of one of the scientists he admired most. The machine that held the only hope he had left.

The machine he was going to reprogram. The machine he was going to turn into something that would get them out of this mess.

He could do it. He _had_ to do it. He had come this far already, and he couldn’t turn back now. He couldn’t abandon his brother. He couldn’t abandon his dad. He would fix this. One way or another, he would make this right.

Soon. Soon, he wouldn’t have to lie to Alphys anymore. Soon, there wouldn’t be anything to lie about.

He just had to finish the machine.


	29. Chapter 24

**Notes for the Chapter:**

> Quick note: though I’ve been trying to update this story every Sunday and Thursday up until now, I’m going to be switching it to just every Thursday, at least until things quiet down for me. Fact is, I’m a (primarily self-taught) student trying to tackle web development, as well as a writer of original novels trying to get my work published, and I’ve been spending so much time on this fanfic that I’m not only not getting other stuff done, but have been stressing out about this more than I’m enjoying it. I adore this story and I love that you guys seem to enjoy it, too, so I definitely want to continue it - I just can’t do it quite as often as before. If things quiet down, I may go back to a twice-weekly updating schedule. Until then, I’ll see you guys next Thursday! Thanks, everyone!!
> 
> And another quick note: the only ships in this entire fic series will be Alphyne and references to past!Asgore/Toriel. Perhaps some Guards 01/02, I dunno. But other than that, everything is platonic.

Papyrus had been the one to bring up the idea of them all having dinner together.

It wasn’t even something Sans thought about nowadays. That had been important once, hadn’t it? Eating together. Now, the only person Sans ever ate with was Papyrus, and that was usually in Papyrus’s room, bringing him dinner or a snack after he came home from a day at the lab. They might have had breakfast together in the mornings, but Sans was usually far too anxious, waiting for Gaster to take his brother away, to get anything down.

And as for eating with _Gaster_ …

Well. The idea hadn’t even warranted a thought before Papyrus mentioned it.

But Gaster, to Sans’s shock, agreed, though it was the sort of passing agreement right before he left for the lab that Sans wasn’t sure if he really meant. The entire day he was out, he expected to come home to an empty house, or just Papyrus, as he did nearly every day.

So it took him a while to process what he was seeing when he walked in the door and found Papyrus setting up the last of what looked like a home-cooked meal on the table, while Gaster already sat in his usual chair, jotting something down in a notebook.

For a second—just one second—Sans swore that the past few months had never happened.

It was his first week of work. His dad had left the lab a little earlier than him, and Sans got back to the house just as Papyrus was finishing dinner. There was hot food on the table, and his family was together. He and his dad would probably talk a little too much about work over dinner, and Papyrus would complain and insist that they leave their work at the lab. Then his dad would make a bad joke and Papyrus would groan and Sans would just smile at how _normal_ it all was.

Then Sans blinked.

Gaster was still marking something down in his notebook, and Papyrus was carrying one more dish to the table, wearing his favorite pink oven mitts, his mouth curled into a shaky but determined smile, the dark circles under his eyes evident even from all the way across the room. There was a bandage wrapped around the top of his skull, which definitely hadn’t been there when he left the house that morning. The plates of food set out on the table were a good deal less elaborate than they would have usually been, as if Papyrus hadn’t had time to go all out—or as if he had been too tired to do so. There was nothing warm about the room, despite the heat still eking out of the kitchen from the coven. It was like looking at a bad caricature of one of the hundreds of family dinners they had shared before, painted with half the usual color pallet, by someone who had never attended a family dinner in their life.

Papyrus looked up as he set the last dish down. His eyes widened for a moment, then he smiled a little wider, standing up straight as if that could hide everything that made this different from all their dinners before.

“Hello, Sans! We’re almost ready to eat! Go ahead, sit down!”

Sans stood there for a moment, still staring. Gaster glanced up from his notebook, long enough to look at Sans before his gaze returned to the table. Sans tried to speak, but he couldn’t think of anything to say. Papyrus bustled back into the kitchen, and after a minute, Sans finally let his bag drop to the floor and crossed the room to the table.

While he once would have flopped down in his seat and started piling food onto his plate without hesitation, now he sat down without any noise at all, and stared at the steaming food like he might stare at a weapon placed in the middle of the table.

Something clinked, and Sans jumped as he looked up to find Papyrus setting a pitcher of lemonade next to all the dishes and taking his own seat to Sans’s left. He took a few seconds longer than usual to settle down, fidgeting as he had more and more lately. Sans found himself checking his HP almost on reflex, and looked away when he found it 3 points lower than it had been the day before.

It took a minute for Papyrus to clear his throat and hesitantly suggest they eat. Gaster looked up from his notebook, paused, then nodded, reaching across the table and adding some casserole to his plate, then filling his fork and sticking it in his mouth. Papyrus followed, and Sans a few seconds later.

It was the same recipe Papyrus had been using for years, but now, it tasted like mush. He ate it anyway.

For at least ten minutes, none of them spoke. They ate, picking at their food at half the normal speed. Gaster didn’t try to start a conversation, and Sans couldn’t decide whether that was more merciful or cruel.

He tried to read his expression, but as usual nowadays, he found it blank.

He came very close to just letting dinner pass by without a word. Maybe that would have been better. Almost definitely, it would have been better. He was too smart to think that saying anything now would change one iota of this mess. But he found his eyes focused on Gaster nonetheless, his voice working its way up his throat before he even had the time to process what he wanted to say.

“So how was work today?” Sans asked, and even though he was sure he spoke no louder than usual, his voice shattered the uncomfortable silence that had overwhelmed the entire room. He folded his hands on the table in front of him, tilting his head in mock interest. “Anything new? Anything interesting?”

Papyrus fidgeted. Gaster didn’t even look up from his plate.

“Nothing worth discussing.”

Sans’s browbone went up, as if he were actually surprised.

“Oh, are you sure? I mean, it’s not like you give me updates anymore. You used to tell us about all the projects you had going,” he went on, allowing a touch of pleading to enter his voice, if only because it made Gaster’s shoulders tense just enough for him to see. “You sure there’s nothing worth talking about?”

“Sans, please,” Gaster replied, putting a hand to his face but still not looking up. He let his fingers trail down over his cheekbones before it fell back to the table. “Let’s eat in peace.”

Sans paused, his eyes flicking to Papyrus, who had stopped eating entirely and now sat small and hunched over, staring at his lap, his whole face tense. And for a second, Sans felt like the bad guy. The one who was ruining this nice family dinner when they hadn’t had any semblance of a nice family dinner in more than a month.

Then he saw the bandages on Papyrus’s head, and gritted his teeth.

“Peace,” he repeated, looking back to Gaster. “that’s a funny word, coming from you.”

Gaster looked at him at last, and Sans flinched, despite himself, caught under the same gaze that had tortured his brother, the same gaze that had peered down at him so gently when he was small, the same gaze that had followed him to make sure he didn’t trip over anything in a new place, the same gaze that had made every cold observation as Sans lay tensed in pain on an examination table.

“Peace is the only thing I ever wanted,” Gaster said, his voice so soft, so genuine, so much like it was before.

But Sans lowered his browbone and stared back at him, his eyes just as hard as before.

“you know, i used to believe that.”

He expected Gaster to look away, but he didn’t. He just kept staring, his face almost pained—even though Sans could hardly remember what his genuinely pained face looked like anymore.

“Nothing about what I want has changed, Sans. As much as you may think it has,” he said. Sans racked his mind for anything he could say in response, anything that made sense, anything that would get across every bit of pain he and his brother had suffered through at Gaster’s hands. But nothing came out. And a few seconds later, Gaster sighed and looked back to the stack of papers sitting next to his plate. “Now please. Your brother requested a family dinner and I don’t think this is what he had in mind.”

Sans flinched. Just for a second, just long enough for Gaster to notice. His eyes drifted toward the third seat at the table, where Papyrus still sat staring at his untouched food, looking more like a small, miserable child than he ever had. Sans swallowed.

Then his eyes narrowed and he turned to Gaster again, giving a pointed look at the notebook sitting next to his plate.

“i don’t think you doing work the whole time is what he had in mind either.”

Gaster’s hand paused in the middle of writing. He looked up, a slight crease in the center of his browbone, his mouth pressed into a tight line.

“The sooner I get this done, the sooner my research will be finished, and the sooner we can all get out of this godforsaken place.”

“You never seemed to mind being stuck in this ‘godforsaken place’ before,” Sans replied.

Gaster didn’t look at him, but his hand tightened around the pen. “You’d be surprised what you can get used to after a few centuries.”

“If you’re so used to it, why did you suddenly start caring so much?” Sans went on, trying his very best to ignore Papyrus fidgeting out of the corner of his eye. “It wasn’t just the cave-in, it _couldn’t_ have just been the cave-in.”

“That cave-in could have killed you,” Gaster bit out, looking at him with such pain that for a second, just a second, Sans couldn’t breathe.

He swallowed, and his browbone lowered again. “and you’re so sure it’s gonna happen again?”

“I don’t have to be sure it’s going to happen again,” Gaster said, a pinch to his face that made Sans’s chest hurt. He turned his gaze down again. “If it happened once, it _can_ happen again.”

He stopped there. He still held onto his pen, he still looked at his notes, but he didn’t start writing. Sans watched him, taking in every detail of his expression, of his posture, everything he had learned about his body language since he was a toddler. And bit by bit, his browbone creased further, his hands tightening around the edge of the table.

“that’s not it.”

Gaster’s eyes snapped back up. “What?”

“That’s not it,” Sans repeated, without a hint of doubt. “You’re not that stupid, _Gaster,_ you were ready to do this before, that just gave you a _reason._ The scales wouldn’t’ve tipped if they hadn’t been lopsided already.”

Gaster’s browbone creased in return, but it was a different sort of expression. Confusion, maybe? Why was it getting so hard to read his face?

“You seem awfully determined to believe that I _want_ to do this.”

“Why else would you be doing it?” Sans spat, a laugh forcing its way out of his throat even as his teeth clenched. “What’s so bad about this place? Why the hell is it suddenly so important that we get out of here that you’d be willing to _torture your own son_? ”

Papyrus whimpered and stared at the table, while Gaster squeezed his pen so hard it almost snapped it half. But Sans paid neither of them any mind. He focused on Gaster, leaning into the table until the edge of the wood dug into his ribs, his browbone so low it almost made his eyes squint.

“Do you think that’s what they’d want? All the skeletons who _died_ in that war? Do you think they’d want to see you _torturing_ one of the only skeletons left? Do you think they’d be _proud_ of who you’ve become?”

Silence. Sans could only make out his own breathing, and a few more faint whimpers from Papyrus, but Gaster didn’t make a sound. He stared down at the table, his face as blank as Sans had ever seen it. Sans huffed and looked away.

“I don’t know.”

Then he looked back, and though he was sure that had been Gaster’s voice, Gaster’s face hadn’t changed. Sans blinked.

“… what?”

“I don’t know what they’d want,” Gaster said, more clearly this time, his voice just as empty. He looked up and met Sans’s gaze, all hints of emotion gone. “I never knew them well enough to find out.”

Sans’s browbone furrowed. Then it furrowed more. He shook his head.

“you weren’t … you told us when you were born. You were a teenager when the war happened, you were basically an adult.”

“Yes,” Gaster replied. “I was.”

Sans stared harder, as if doing so might make what his dad was saying make any more sense. “So you had plenty of time to know them. You had plenty of time to know that—”

“You seem awfully sure about that for someone who wasn’t there,” Gaster snapped, and Sans found himself tensing on reflex. Had he ever heard his—had he ever heard Gaster’s voice sound that bitter? Had his eyes ever looked so hard? “You seem awfully sure of what those other skeletons would have wanted, for someone who never _knew_ any of them.”

Sans just shook his head again, leaning away from the table so his ribs had more room to move when he breathed.

“How could you not have known them? They were … you had a family, didn’t you?”

“Yes. I did,” Gaster said. His eyes burned into Sans’s goal, so hard that Sans swore he could feel his soul aching in his chest. “And after the age of six, I saw them less than half an hour each day. And the other skeletons even less.”

“What the hell are you talking about?” Sans asked, his eyes wide enough to hurt. He could just make out Papyrus looking back and forth between them, but without shifting his gaze, he couldn’t tell whether he was more curious or upset.

Gaster just stared at Sans, in something in between pity, offense, and disbelief.

“Do you think the childhood you had was anything like mine?” he asked, so calm it made Sans shiver. “Do you think that my family made any _semblance_ of the effort to understand me as I have both of you? Do you think I had _anyone_ who was like me, anyone in my own species who understood how I thought, anyone who _listened,_ even though they had no trouble hearing me when I spoke?”

It took a few seconds for all the words to register in Sans’s head. It took a few seconds for the few extra words, the words that really shouldn’t have needed to be there, to stick out. He blinked.

“Anyone in your own species?” he repeated.

Gaster’s face twisted and tensed, and he looked away. Sans couldn’t even bring himself to feel satisfied seeing him in pain. Not if he didn’t know _why_ he was in pain.

“The history books don’t care to mention what things were like before the war.”

Sans sat up a little straighter in his seat, feeling a bit like an undergraduate again, sitting in the front row, searching for any question he could answer.

“They said … there was a lot of tension,” he said at last, with more uncertainty than he had ever answered a question in class. “Between humans and monsters. For decades. Centuries.”

“Yes. Tension. That doesn’t mean they never spent any time together,” Gaster replied. He looked at Sans, then looked away again, though not quick enough to hide the emotion gleaming in the backs of his sockets. “That doesn’t mean none of them were ever friends.”

“Friends?” Sans asked. Papyrus was definitely watching Gaster now, his eyes locked on him as firmly as Sans’s. “You were friends with a human?”

Gaster sighed. For a minute after that, he said nothing. Sans waited. He didn’t even try to think of anything else to say. Anything else to ask. Gaster’s silence was all the answer he needed.

At last, Gaster looked back to him, and Sans almost flinched from the bitter ache in eyes that had never looked quite so old.

“Have you ever thought about what it’s like, for no one to be able to understand your font?” he asked. Sans didn’t respond. Gaster gave a barely-visible shake of his head. “You two were lucky. That was what I hoped for you, what I _wanted_ for you, that it wouldn’t _matter_ that you were two of the only skeletons left, you could speak to _anyone_ without any trouble, without needing to sign, you would never have any trouble making yourself understood.”

His mouth pressed into a tight line, and he looked at Sans, for just a moment, like Sans had taken away everything he had ever held dear. Then the look was gone, before it could even begin to sink in.

“No one understood me. No one except for the skeletons, and all they could understand was my speech, they couldn’t understand what I _said._ ”

He swallowed, loud enough for Sans to hear him across the table.

“She did.”

Sans’s browbone was twitching now, unsure whether it wanted to rise to the top of his forehead or fall down into his eyes. “A human understood you.”

Gaster’s mouth twitched up at the corners, as if he might smile. It almost looked happy.

“It took her three years,” he murmured, more to himself than to anyone else. “Three years of studying everything that came out of my mouth, three years of word games, three years of spending _every day_ with me, but she could understand. She understood perfectly. She spoke and I spoke and she understood _everything._ ”

“And she was your friend,” Sans said. It wasn’t a question.

Gaster looked at him again, his eyes so old, like he might fall down any second.

“Yes,” he breathed. “And then the war started.”

Any words that had been building in Sans’s throat died then and there. Gaster’s mouth pressed into such a thin line that Sans could hardly make it out against the white of his skull.

“And she promised that no matter what the other humans did, she would never harm me. Me or any other monster. She _promised_ that she would never join them. No matter how bad things got.”

Gaster had never sounded so old, and he had never sounded so young. Like a teenager. Was this what his dad had sounded like, when he had been a teenager? A teenager thrown into the middle of a war? A teenager who was about to lose everything he had ever known? Gaster stared down at the table, setting down his pen before he actually snapped it in two.

“She promised,” he murmured, like a small child crossing his heart. “And she lied.”

Sans swallowed against the lump in his throat. Gaster looked up, and Sans couldn’t move.

“I trusted a human, because she took the time to understand me. I trusted her because I had spent every day with her for eleven years,” he went on, his voice blank, the hints of emotion dying with each word that slipped past his teeth. “Then I found her covered in my brother’s dust.”

Papyrus made a faint noise, something like a whimper, cut off before it could turn into a full cry. Sans wanted to get up and comfort him, hold him, even just pat his shoulder. But he couldn’t move. He couldn’t do anything but stare as Gaster pinned him in place with only his gaze.

“Every other skeleton died in that war. Every. Single. One. But I was too scared to fight. I stood there, because I had spent so many years trusting a human that I couldn’t _process_ what she had done, she had _murdered_ my brother and I let her go, I just stood there and watched the humans slaughter every member of my family, every member of every skeleton family in existence. But not me.”

His eyes fell down, down to the table, down to his lap, down to the floor below.

“Not me.”

It was hardly a breath, and for a second, Sans wondered if Gaster had forgotten he was talking to someone else. With each second, he looked like he had slipped further away, further back, closer to a time Sans had only ever known about through history books. A time only a small handful of people in the Underground remembered at all.

Gaster gritted his teeth and curled his hands into fists on the table. “And I watched as the humans forced us underground, I watched as we all saw our last glimpse of the grass, the trees, the sky, the stars, the _sun,_ I watched as everyone around me tried to figure out which of their loved ones was still alive and I knew _no other skeleton would ever come,_ because they had _died._ Because I had trusted a human too much to protect them. And I didn’t even know how to miss them because I had never taken the time to _know_ them.”

His fists trembled, and a faint glow flashed in his eyes. Sans had never seen his dad’s eyes light up. He was always so controlled, he never let his magic flare, not even in his most panicked moments. Even now, it disappeared before he could make out the color.

“And I spent two thousand years wondering what I could have changed, wondering what they had been like, wondering what I had missed, clinging to every scrap of skeleton history, because I knew _there would be no more._ ”

He looked up again, and again, Sans couldn’t move. But this time, Gaster looked at Papyrus as well, and when Sans followed his gaze, he found Papyrus hunched over, his arms wrapped around himself, looking at Gaster with sockets wide enough to make him look five years old all over again. Gaster’s eyes softened, and Papyrus’s face softened with it, and god, Sans hated Gaster, he hated him with everything he had, so _why did he still want to reach over and pull them both into a hug_?

“And then there were,” Gaster breathed, with such affection that it hurt to listen to. “Then there were two more skeletons, and they were mine, and I had no idea how to take care of them, but I …”

He swallowed, shaking his head, so unsure, so lost, how could someone look so old and so young at the same time?

“I couldn’t let them go.” A faint, humorless chuckle forced its way out of his throat. “They were everything. And I wanted to _give_ them everything. Everything I had never given the others. Every year, every day, every _minute._ And I didn’t even know how to raise them like skeletons _should_ be raised, because _I didn’t remember,_ you are the _only_ skeletons I have ever really known, the _only_ skeletons I have ever loved, because I was too focused on _one damn human_ to protect the people I should have stood with from the moment that war began.”

He let out a long breath, the air trembling as it fell past his teeth. He looked at them, just looked at them, for more than a minute, as if taking in every detail. Sans felt like he was being probed from the inside out. The line of Gaster’s mouth twisted and his brow tilted up in the center.

“I could do better. I could love you like you should be loved. And I could make sure that you would be understood, you would never feel alone, you would never feel anything less than proud to be skeletons,” he went on, his voice soft, his eyes shifting to Papyrus, then to Sans, then back and forth between them every few seconds. Papyrus fidgeted. Sans wished he could make him never look at Papyrus ever again. Gaster sat up a bit straighter, his sockets pained. “But I knew that no matter what I did, no matter how hard I worked, you would still never get to see what you had missed out on. You would _never_ get to see that sun, you would _never_ know the grass or the trees or the sky or the stars because I _let_ them take it away from you.”

He folded his hands over one another and squeezed them, so tight Sans wondered if it was possible for him to snap his own fingers off.

“Then I found out you could. If I tried hard enough. I could get you _out,_ I could let you see _everything_ you missed, I could give you the life you should have had, the life I should have given _them,_ the life I can give _you,_ the life those damn humans stole from every one of us, the life you _deserve_.”

Gaster looked at Sans once more. His browbone lowered, his teeth gritted, his eyes burned.

“So don’t you ever suggest that I _want_ to hurt you,” he hissed, so different, so similar to the man Sans had called “Dad” that it hurt to look at. “Don’t you ever suggest that I want _anything_ other than to give you everything you should have had from the beginning.”

Silence.

His dad stared at him for a few seconds longer, then looked back to his plate. His folded hands softened. He glanced at the papers at his side, as if he might go back to them, but apparently decided against it.

No one took a single bite of their food. Papyrus had sunk down so low in his chair that he looked as if he might disappear at any second. The steam that had risen from the food at the beginning of the meal was gone, and Sans wouldn’t have been surprised if his own had gone completely cold. It felt like he was trying to breathe through gelatin, the air thick and sticky, everything heavy and pained.

Still, he found his chest burning, the words bubbling up in his throat before he could even hear them in his head.

“We’re not replacements.”

Gaster looked up, a touch of surprise on his face. Sans could see Papyrus looking toward him out of the corner of his eye, but he kept his gaze firmly on Gaster.

“We’re not here to replace the people you lost,” he went on, and it hurt to speak, it hurt to form every word, it hurt to _look_ at Gaster and see a face he had once loved more than almost anyone in the world, but he never looked away.

Gaster’s browbone creased. “I never thought you were.”

A tiny part of Sans tried to believe it. But the rest of him looked at Gaster, heard his words echoing in his head, the rest of him looked at this man that he had once called his father and heard every word he had said and felt the last nineteen years of his life rip out from under him.

“Is that all we ever were to you?” he asked, his voice almost quiet enough to count as a hiss. “Just two more members of your species, here to make sure you weren’t _alone_? A way for you to make up for the fact that you fucked things up so bad with the skeletons you knew before? ”

Gaster jolted, like he had been zapped. Hooked up to the same machine that electrocuted Sans, just to see whether he would react the same as a human.

“Stop it—”

“If you’d put a piece of some other monster in that jar and they’d grown, would you have just given them up?” Sans cut him off.

Gaster stared at him, so pained that Sans almost wanted to stop, _almost,_ but this wasn’t him, this wasn’t his dad, not anymore, not ever again. “I wouldn’t have—”

“Is that the only reason you kept us?” Sans went on, leaning closer over the table, the wood digging into his ribs once more. “Because we were the only other skeletons left? Is that what you saw every time you looked at us?”

“I—”

“Did you ever stop to think about what we want? _You_ think it’d be worth all this to get to the surface, but did you ever ask us?”

“Yes. I did,” Gaster bit out, eying him with narrowed sockets. “And you told me it would be worth whatever it took.”

Sans stood up, so fast his chair almost fell over, and threw his arms out to his sides.

“I didn’t mean _this_! ”

Papyrus stiffened. Gaster just stared. Sans huffed so hard his ribs hurt, his head spinning, his soul clenched, but he didn’t care, he didn’t care about anything, he didn’t care about that stupid machine that might not even work, all he wanted was to look in his dad’s eyes and make him _listen._

“Do you think everything’s just gonna go back to normal once you’re finished? Do you think we’re just gonna _forget_ all this happened? Do you think we’re gonna live all happy and peaceful on the surface after _everything you did to us?_ ”

Gaster’s hands clenched together on the table. Sans’s browbone lowered even further.

“You didn’t think about _that,_ did you?” he asked, barely louder than a whisper. “You didn’t think about when this _stopped_ being what we wanted? You don’t even care what we want, you think just because _you_ wanna get to the surface so bad, we must want to too! You think because we’re the last skeletons that we _have_ to see the surface or else you’ve failed your species! I don’t know if you’ve noticed, but we’re _not_ the skeletons you knew two thousand years ago! We were _born_ down here, this is all we _know,_ and we were _happy_! We were happy until _you_ screwed it all up!”

Nothing. Not a word, just staring back at him and Sans wanted to kill him, he really wanted to kill him, he wanted to end all of this, he didn’t need him, he didn’t need this, all he needed was Papyrus, then everything would be okay. His eyelights went black.

“but maybe it’s good we finally get to see this. finally see what you’re capable of. We finally get to see the _real_ you. What you really think of us.”

Gaster straightened. “I _love_ you—”

“no you _don’t_! ” Sans shouted, loud enough for his voice to echo around the room. “You just love the idea of not being a lonely old man! You love the idea that you can make up for failing _them_ if you don’t fail _us_! You love having something to remind you of everything you lost! You love the idea that you don’t have to die _the last skeleton who will ever live_ —”

“stop it, sans!”

And Sans stopped.

Because Gaster hadn’t spoken.

His mouth hadn’t moved. And that wasn’t Gaster’s voice.

Sans turned his head to the left, to where Papyrus sat hunched over in his chair, his arms close to his torso, his head hung low as tears streamed down his cheekbones, dripping down into his lap.

His breath hitched with suppressed sobs, and all Sans could do was stare as he shook his head, over and over, hugging himself tighter as if that would somehow shield him from the tension in the room.

“please … please, stop …” he breathed.

Sans looked at him. Just looked at him. He felt his hands begin to shake. He felt the tension in his shoulders begin to slip away. He felt himself sink into his chair.

And he felt Gaster’s eyes on both of them, shifting between them, just as unreadable as ever.

He said nothing else.

None of them spoke for the rest of dinner. They ate, a little. Sans poked at his food, and Gaster wrote in his notes, and Papyrus sat there quietly crying for another few minutes before he picked up his fork and ate half of his meal. He never seemed to have much of an appetite nowadays. Sans had never figured out whether it was a side-effect of the experiments, or just too much stress.

He doubted Papyrus knew any better than he did.

It was Papyrus who finally pushed himself to his feet, pick up the still-loaded plates, and carry them to the kitchen. Gaster glanced up at him, his expression somehow pained, but looked back to his notes a second later. Sans stared at him, searching for any sign of the man who had once picked up on the slightest signs of upset in either of them, who had brought them desserts and toys and kind words until they felt better, even if he could never figure out what the problem was.

He tried to imagine what was going through his head right now, but his own mind came up blank.

Papyrus washed the dishes, and halfway through, Sans stepped up next to him to dry. Papyrus glanced at him, but said nothing. His hands were shaking as he picked up each plate—apparently he had already scraped up the remaining food and put it back in the fridge. He always was big on conserving resources. Everyone in the underground was, to some extent, but Papyrus had always taken it more seriously than any of them. Maybe because he had been the only one in charge of the house for so long.

For the first time, Sans found himself wondering if Papyrus would have rather spent his time doing something else.

When the dishes were clean and put away, Sans returned to the main area of the kitchen to find Gaster still sitting there, staring down at his notes. Sans started to speak, but then remembered Papyrus standing behind him and cut himself off. Besides, it wasn’t like he could think of anything to say.

But while he walked past the table and started into the living room, Papyrus approached the table and stopped. He stood only a few steps away from Gaster, but Gaster didn’t acknowledge him. Papyrus fidgeted. Nothing. Sans gritted his teeth to hold back the remark that now tried to force its way out of his mouth.

“um … dad?” Papyrus asked, his voice still quiet, shaky and a little bit broken, as if the tears had scratched up his throat, even though Sans knew that made no sense for a skeleton.

Gaster looked up, pausing, as if he hadn’t realized Papyrus had even left the table.

“Yes, Papyrus?”

Papyrus looked down at his feet, clutching his shirt. Sans didn’t dare look at Gaster’s face. He didn’t want to see whether his eyes softened at such a nervous, uncertain gesture. He didn’t want to see whether the affection from before turned up, even for a second.

“do you think I … could maybe … sometime …” Papyrus swallowed hard and looked up. “Could I go outside by myself?”

Sans stiffened, and his eyes shot back to Gaster before he could stop himself. Gaster just sat there, silent, for almost half a minute. He didn’t say anything, and as hard as Sans searched his expression, he couldn’t find anything that betrayed what he was thinking.

But then that half-minute ended, and something softened in Gaster’s eyes, and Sans had never felt more conflicted since the day he was born.

“Yes, I think that would be alright,” Gaster said, giving a small nod before turning back to his notebook.

Papyrus’s eyes lit up. Sans wanted to die.

“Really?” he asked. Gaster’s shoulders stiffened, but all he did was give a small nod. Papyrus’s face brightened even further. “Wowie! That would be so much fun! I really missed going outside. I mean, I go outside almost every day, when we’re going to the lab, but it’s not for very long and it’s always the same stuff and I’ve really missed going to Waterfall and Snowdin and the Capital. Hotland gets very boring if it’s all you see!”

Gaster’s head tilted further away. “Hm.”

Papyrus’s face fell a bit, just a bit, as if he had hoped for a more enthusiastic response. Maybe even an offer to take them out for the day, on a family trip, even if they hadn’t gone on a family trip in at least a year. His mouth hung open for a few seconds before closing again. Gaster’s grip tightened on his pen, but he said nothing else. If Sans looked closely enough, he swore he could see his gaze lifting for just a second, not quite long enough for Papyrus to see. Sans found his own browbone furrowing, and for the same second, he tried to figure out how it had been so easy. But the answer came to him even quicker than the question itself.

Gaster knew Papyrus. He had _raised_ Papyrus. He had known Papyrus well enough to be sure that he would go along with this. That he would put up with the worst of it. That he would defend his dad no matter how things got.

And he knew that Papyrus would never tell anyone.

He had known that from the beginning, hadn’t he?

When Papyrus had walked home every day, by himself, perfectly capable of going to tell someone what was happening to him, if he had wanted to.

But he hadn’t.

And he wouldn’t.

Sometimes Sans wondered whether his brother had even thought of it.

Whether he had decided, just like Sans, that he couldn’t bring himself to face the consequences.

Sans watched as Papyrus started out of the kitchen. He walked up to Sans and wrapped his arms around him, just like he did every evening, no matter how tired he was. And Sans hugged him back, because it didn’t matter if he was angry or confused, he wasn’t going to deprive his brother of anything he wanted if it was in his power to grant it.

For the first time, he found himself wondering what hugs from other skeletons would have felt like. Skeletons who were nothing but faceless, nameless blurs in his head, but had never felt more real.

Papyrus stepped away after a minute, and looked at Gaster, who had finally stood up, and now lingered near the entrance to the kitchen. Gaster stared back. There was something … different about his eyes. Something sadder. Something Sans swore he had never seen before, even before everything had gone to hell.

His hands twitched at his sides, like they once had before he lifted them to draw Papyrus in for a hug.

Papyrus took a step toward him, his eyes wide, his own hands beginning to rise as well.

Then Gaster froze, his hands frozen, trembling, for just a second before they dropped back to his sides. Papyrus’s face fell.

But he didn’t speak. He just turned around and walked up the stairs, slipping into his room, pulling the door shut behind him.

Sans stood there for at least a minute, staring at the door and debating between running up to comfort his brother and staying right here. In the end, a soft sigh made the choice for him, snapping his attention back to Gaster, who watched him with dull eyes that made Sans believe, just for a second, that he was hurting as bad as they were.

“You were never like the others,” he said, and for once, he sounded exactly as old as Sans knew he was. Exactly as broken. Exactly as lost and alone. His eyes were so soft he could almost forget any of this had happened. As soft as his dad’s had been, before Sans had taken his first step into the lab. “You were always far too much like me to be like them.”

Sans didn’t notice his hands curling into fists until they began to tremble his sides. Gaster pressed his mouth into a thin line and sighed.

“And you were always the best thing that ever happened to me.”

His eyes rose to the top of the stairs, the closed door he hadn’t passed through in more than a month.

“Both of you.”

Sans started to speak, but the words died in his throat before he could even figure out what he was going to say.

Whatever it would have been, he never got the chance to try again. Gaster gave him one more long, lingering look, then pressed his mouth into a thin line, walked up the stairs, and shut himself in his office, locking the door behind him.

And Sans was alone once more.


	30. Chapter 25

Sans had never cared much about Fridays before, at least not over any other day of the week.

He had enjoyed school, and for a while, he had enjoyed work, so unless he had something special planned over the weekend, there was no reason to look forward to the week ending. But now he despised Fridays above any other day of the week—though not quite as much as Saturdays and Sundays.

Because the weekend meant that the other scientists would be out of the lab. The entire building would be empty for two whole days.

Giving Gaster absolutely no reason to make sure Papyrus didn’t scream.

During the week, at least during the day, he had to keep things somewhat quiet. The building was big, without a doubt, but his lab wasn’t soundproof, and if Sans had been able to hear Papyrus screaming from a closet down the hall that first evening, he had no doubt that Dr. Japer, Dr. Frewth, Dr. Lemming and anyone else who happened to walk through the underground portion of the lab would be able to hear it, too. That was why Gaster usually did the worst experiments in the evenings, and did the “easier” procedures throughout the day.

But during the weekend, no one came to the lab. Gaster was alone with Papyrus for two days, and during those two days, he could fit in all the new experiments he had thought of during the week.

Sometimes Sans caught himself wishing that one of the other scientists would come in and find out exactly what he was doing.

Then he caught himself and pushed the thought away, as hard as it tried to come back.

He was already resigned to the days to come when he left his lab on Friday afternoon, having spent the day working through the program Alphys sent him. Usually, Gaster let Papyrus stay home on Friday evenings, so maybe, he could at least give his brother a nice, relaxing, comfortable few hours, and a long restful night of sleep, before he had to go deal with a full day of torture.

Papyrus always seemed to appreciate it.

Even if Sans could never let enjoy it himself.

He pushed open the door, and listened for a moment for the telltale signs of footsteps anywhere in the house. Papyrus had stayed home today, hadn’t he? No, wait, Gaster had given him permission to go outside. That was what Papyrus had said this morning, repeated it for the fifth time since last night. He was so excited. He was going to go to Snowdin and Waterfall. He had gone on and on about it to Sans, but all Sans could do was watch Gaster as he slipped out the door, and begged everything he didn’t believe in that he wouldn’t change his mind.

Gaster left without a word.

With any luck, Papyrus had had a nice day out sightseeing, exploring some of his old favorite places. Hopefully, it had been a good day.

But … it already past five.

Sans listened, but he heard nothing.

“papyrus?” he called out, his voice echoing through the house. “bro, you home yet?”

Nothing.

Well … if he was enjoying himself, there was no reason why he should hurry back.

He should enjoy as much time away as he could.

Sans considered trying to fix dinner, but every time he opened the refrigerator, searching for something he could make, he found nothing. Papyrus hated frozen dinners, and though Sans checked every cabinet, they were out of fruity cereal. When had they run out of fruity cereal? Why hadn’t he noticed they had run out of Papyrus’s favorite food?

He should go and get some. He should go and get some and have it ready when Papyrus got home.

But … what if he wasn’t back by the time Papyrus got home?

Papyrus had always said it was Sans that made him feel better, more than anything else. And if Papyrus wanted him to be home, then he should be home.

He would get more cereal tomorrow, after Papyrus went to the lab.

He sat down on the couch, settled into the corner close to the arm, stared at the door, and waited.

He wasn’t sure how long he sat there. There was no clock in the living room, and he didn’t feel like getting up to check the one in the kitchen, even though it might have made him feel better—or worse. He just watched the door.

It had been an hour, at least. Or two. He wasn’t very good at telling time nowadays.

Papyrus should be back by now. Gaster sometimes stayed late, but Papyrus should definitely be back by now. Had Gaster changed his mind and brought him to the lab after all? Was there some kind of unusual experiment going on? Was Papyrus hurt? Of course he was, he was always hurt nowadays, but was he hurt worse than Gaster could heal?

How much _could_ Gaster heal, anyway? Had he tested that? Had he ever had a chance to test it?

Would he want to test something like that next?

Sans gripped his arms a little tighter, not sure when he had started hugging himself in the first place. He sunk a little further into the couch and tried to reign his thoughts in, even as they raced off into thirty different directions. He still didn’t know all the things Gaster did to him. Papyrus didn’t talk about it. He didn’t like to talk about it. Maybe Gaster had truly lost it and started doing life-threatening experiments. Maybe … maybe something really had gone wrong. Maybe something that gone wrong and Gaster hadn’t been able to heal him and Papyrus had—

The door opened, and Sans jolted up so hard his head rushed.

And Papyrus poked his head in through the open door.

Sans’s shoulders fell fast enough to make his whole body fall to the floor.

But while Papyrus normally would have strode inside—or slumped in with his best attempt at a smile, as he had more recently—this time he didn’t even turn to face the living room. He slipped in part of the way, his eyes focused on something on the porch, gesturing toward himself, as if beckoning someone forward.

“Come on, it’s this way.”

Sans’s browbone furrowed, but he didn’t have time to think about what the hell could be up before Papyrus stepped inside, and something followed him, standing just to his right as he let the door shut and held his arms out to his sides, like he was showing off a work of art.

“Welcome to my house!” he announced, almost as loudly as he had spoken every day before this whole mess began. “This is our living room. And those are our stairs and that’s our kitchen. And that’s our couch, and that’s my brother, Sans! Hello, Sans!”

Sans didn’t say anything. He couldn’t make his voice work, he couldn’t make himself move, he could barely make himself _breathe._

Because there was a human standing in their doorway.

A small human, no taller than himself, with curly, bright orange hair and a funny hat, looking around at the living room in something between curiosity and fear.

If Papyrus noticed Sans’s wide, frozen eyes, he said nothing about them, holding his arm out to gesture to the human with the widest grin Sans had seen on his face in weeks.

“This is my new friend,” he said, looking down at the human and smiling wider. “I found her wandering around and she said she had never been to Hotland before and didn’t have anywhere to sleep so I told her she could stay here.”

The human looked back to Sans, its eyebrows furrowing as it brought its hands close to its chest and stood up a little taller. Sans pushed himself the rest of the way off the couch, slowly, but quickly enough not to risk the human moving before he had the chance to act. Both of them kept their eyes locked on one another, following every twitch, every breath. Sans glanced at Papyrus for under a second, just long enough to make out the vaguely confused, yet still pleased, gleam in his eyes.

“bro … that’s a human,” Sans said, his voice as slow and clear as his movements.

Out of the corner of his eye, Papyrus straightened.

“What?”

“That’s a human,” Sans repeated, a little more loudly, running a quick internal check on himself to make sure he at least had enough magic to summon some bones. “There. Standing right next to you.”

Papyrus turned to face the human, his sockets wide, though instead of the fear, the wariness, Sans would have hoped for, he just looked curious.

“Are you a human?”

The human stood a step back. It glanced at the door, at Sans, then back at Papyrus, as if guessing whether it would be able to get out the door before anyone caught it. It shifted from side to side and brought its arms closer to its torso, its gaze falling to the floor. Maybe it had lied to Papyrus this whole time—or at least avoided the truth—but it was smart enough to know it couldn’t lie to Sans.

It swallowed, loud enough for Sans to hear from across the room.

“… yes.”

Papyrus’s browbone shot up so high it almost disappeared off the top of his head. Then he beamed.

“Wowie, a real human!” he nearly squealed. “I never thought I’d get to meet one. So that’s what they look like. Do all of them have hair like yours? It’s very bright and pretty.”

He tilted his head, sockets wide, still smiling, as he peered closer at the orange curls that poked out from underneath the human’s hat. The human peered up at him from under the brim, brow creased, but raised a bit, unsure. Sans took another step forward. The human’s eyes snapped toward him, and Papyrus followed, his smile slipping when his gaze fell on his brother.

“Sans, what’s wrong?” he asked, confused, oblivious, god, for once in his life, why couldn’t Papyrus just _see_ when there was danger right in front of him? Sans’s fingers twitched at his sides, one of his hands readying to grab the human’s soul at a second’s notice. The human curled up further. Papyrus straightened. “Sans, what are you doing?”

Sans moved again. His hand lifted, just a bit, just enough for the human to make it out.

“get away from it, papyrus.”

Papyrus looked down at the human, then back at Sans, his browbone creased. “what? Why? She’s my friend.”

“it’s a human,” Sans said, without taking his eyes off of it, even as it shifted back toward the door. “humans are dangerous.”

Papyrus paused. He looked at the human again. Sans. Human. Sans.

“Oh.” He fidgeted, but finally pulled himself up a bit taller, doing his best to smile even though it came out forced. “Well … this one isn’t. I’m sure of it.”

It was the first time in a very, very long time that Sans had actually wanted to yell at his brother.

“Papyrus,” he bit out. “You remember history class. you know what humans are like. you know what they do. You know what they’ve _done._ ”

They had just talked about it last night. Just heard everything Sans had learned in history class confirmed.

Humans were cruel. Heartless. They hurt and killed and took and _took_ until there was nothing left.

They had started this whole mess.

And there was one _right there._

Papyrus’s smile disappeared entirely now. Sans hated himself as he watched that glee begin to slip away, replaced by the same anxiety he had done his best to calm over the past few weeks. The same anxiety this _human_ had apparently managed to calm in less than a day. Papyrus wrung his hands in front of him.

“But … but she’s nice. She looked a little scared when she first saw me and she shouted a lot but then I introduced myself and told her I just wanted to help and she got a lot nicer after that. And when I told her I wasn’t feeling very good on the way here she gave me some of her food and I felt much better.”

He tried to smile again, but this time, he couldn’t manage it for more than a second at a time. Sans shifted a little more forward, only a few yards away now, his hand raised so far that Papyrus finally began to notice it.

“Sans,” he said. Sans didn’t reply. “Sans, you’re … Sans, stop looking at her like that.”

Sans grit his teeth and pinned the human in place with his gaze. “just because it did one nice thing for you—”

“She.”

Sans paused, browbone furrowed, and finally allowed his eyes to shift back to his brother, even though they returned to the human mere seconds later.

“what?”

“You keep calling her an it. She’s not an it. She says she prefers she,” Papyrus replied. He stood up a little straighter, and his face twisted into something between disapproval and concern. “And … and I won’t let you be mean to her, Sans. You’re my brother, but that doesn’t mean you can be rude.”

Sans started to talk, looking back and forth between Papyrus and the human, as if that could somehow get across everything he couldn’t put into words. But his voice caught in his throat, and he just stood there, staring, wracking his mind for a way to make Papyrus understand.

There was a human. A real human, standing in their living room.

A _living_ human, standing in their living room.

All this time, Gaster had been measuring the similarities between Sans’s and Papyrus’s souls and that of the single human he had on record, the one he had been able to research before its soul was extracted. He had done a good bit of research, enough to have a firm baseline, but that was _it._ That human was dead. He could research its soul, he could even extract different elements _from_ the soul, but it was never the same. He would never be able to learn as much as he could from a real, living human.

But now …

The soul was here. They already had five, this would make six, it meant they would only have to synthesize _one_ human soul in order to get out of here. And with what could be learned from another human, given how much Gaster already knew …

He kept saying that he was doing this to get them out of here. That his experiments on Papyrus were so essential only because it was their best chance of breaking the barrier.

If that changed … if Papyrus _stopped_ being their best chance of breaking the barrier …

If Gaster had something else to focus on, something more interesting, something more promising …

Sans straightened up a little, trying to smooth his face into something reassuring, even as both the human and Papyrus watched him with wide, wary eyes.

“It—she can’t stay here, Papyrus,” he said, in as reasonable a tone as he could manage. He took a step forward, lifting his hands from his sides, slow enough so it wouldn’t look like a threat. “Give her to me, I’ll take her … somewhere else.”

Papyrus stared, and Sans forced back the memory of every time Papyrus had told him how bad it was to lie.

“somewhere better for her.”

The human stiffened and watched him, frozen, unsure, but Papyrus put his hands on its shoulders and tugged it a little closer.

“no,” he said, shifting himself in front of the human so it almost stood behind him. He held out his arm in front of it and pressed his mouth into a tight line. “You’re going to do something bad. You’re going to hurt her. I won’t let you hurt her, Sans!”

Sans stepped back. Just a tiny step, but enough for Papyrus to notice. He tensed, but he did not back down. Sans shook his head.

“pap, i …” But there was nothing to say. Nothing that would matter. Papyrus kept staring, such defensiveness, such fear, such determination in his eyes that for a second, he hardly looked like himself. Yet at the same time, he looked more “Papyrus” than he ever had before. Sans’s shoulders slid down, and he felt himself nod before he even realized he was doing it. “okay. Okay.”

The tension in Papyrus’s bones slipped away, and he smiled, hesitant, small, but still a smile.

“Good.”

He looked down at the human, smiling wider now, his eyes a little brighter as it stared up at him with an unreadable face. He patted its head.

“Don’t worry, human friend. Sans is really nice, he’s just been … a little jumpy lately. You’ll get along very well soon, I know you will,” he said. He glanced at Sans, just long enough for Sans to see the pleading in his eyes. Then he turned to the human once more, taking its hand and leading it up the stairs. “Now, this way! I’ll show you my room. You can sleep in there for tonight. We could make a bed for you on the floor or you could sleep in my bed. Oh! Or we could build a pillow fort and sleep in that. Sans and I used to make those all the time when we were babybones.”

The human followed without complaint. Without a single word. Only once, at the top of the stairs, did it glance over its shoulder at Sans, but it wasn’t long enough for Sans to tell what it was thinking.

Then both of them disappeared into Papyrus’s room, the door closing behind them.

Papyrus hardly ever closed his door.

Sans stood at the base of the stairs, staring after them, for at least five minutes. Every time he tried to think, his mind seemed to shut down, and every image in his head was replaced by Papyrus standing in front of that little human, as if it was the helpless victim, and Sans was ready to kill it in cold blood.

Except …

He glanced behind him at the front door, and locked it. It wouldn’t do any good. Gaster had a key. But it felt better to lock it. It felt better to feel like he would have a few extra seconds if he needed them.

He risked one more look at Papyrus’s bedroom. If he listened hard enough, he could make out the faint sounds of talking from the other side of the door. Papyrus’s loud voice, and another, smaller, more feminine, hesitant at first, but slowly growing more confident, as almost everyone did when Papyrus had a chance to encourage them.

Sans listened. He looked at the lock on the door, and wondered if a few seconds would make any difference at all.

He wondered, this time, if he even wanted it to.

Then he went up to his room, closed the door, laid down on his bed, and tried to drown out the two voices echoing through the walls and pounding into his head.

**Notes for the Chapter:**

> Though this wasn't directly based on it, I realized after I wrote this chapter that it holds several similarities to Randomcat1832's story, [Red on White](http://archiveofourown.org/works/8300176), and may have been subconsciously inspired by it. Either way, it's an awesome story and you should go read it. ;)


	31. Chapter 26

**Notes for the Chapter:**

> Before you read, check the tags again. All of them. Anything that triggers you? Anything that might genuinely upset you? No? Okay, then, proceed! (Stay safe, everyone!)

Sans didn’t sleep more than an hour that night.

Every time he began to drift off, he found himself snapping awake, scrambling out of bed and poking his head into Papyrus’s room to make sure that he was still there. That they were _both_ still there. That the human hadn’t hurt him.

Every time, he found the human curled up close to the wall in Papyrus’s bed, while Papyrus lay on his front on the floor, sprawled out in his sleeping bag, lopsided and gangly with his limbs stretching every which way.

Every time, he swore the human’s head tilted a little toward him, as if it had heard him come in, but didn’t dare turn to face him.

Sans got out of the bed for good around 6:30, and sat on the edge of his mattress, fidgeting, for at least a half-hour. Then he went downstairs. He wasn’t sure why. He wasn’t going to eat anything. Food had never sounded more unappetizing in his entire life. But he couldn’t stand to stay in his room any longer, and even if it was more suspicious than anything to sit on the couch all morning, it was better than the alternative.

He heard the first sounds of movement from Gaster’s home office—which basically counted as his bedroom nowadays—a little after seven, but the door never opened. Gaster never came down for breakfast nowadays, so he didn’t notice when Papyrus slipped into the kitchen and filled two plates with food, then carried them back upstairs. Maybe he wouldn’t have cared even if he saw it. It wasn’t like he seemed to care much about what they did as long as it wasn’t affecting his schedule.

Sans stayed in the living room, looking back and forth between the door to Gaster’s home office and the door to Papyrus’s bedroom, waiting to see which one would open first. His legs twitched to check on the human, to make sure that nothing had happened, even though every logical part of him said that humans weren’t stupid, and that one was certainly smart enough to know that attacking Papyrus now would mean sealing its own fate.

That didn’t make Sans’s legs twitch any less.

It was 7:30 when Gaster’s door finally opened.

He didn’t seem to notice Sans sitting on the couch on the ground floor. He was already dressed for the day, and he went straight to Papyrus’s bedroom, knocking on the door and calling out briefly for him to come along, with the tone that suggested this had become a routine. Sans tensed. But Gaster didn’t wait for Papyrus to open his door, and when Papyrus cracked the door open, Gaster was already starting down the stairs.

He wasn’t paying enough attention to see Papyrus frown, poke his head back into the room, and whisper something before closing the door behind him.

Papyrus followed, but while Gaster kept going until he reached the front door, Papyrus stopped at the top of the stairs. He fidgeted, glancing back toward his bedroom. Then his eyes fell on Sans, just for a second, but long enough for the silent plea to reach him. Gaster paused, as if he seemed to have realized he was no longer being followed, and turned around. Papyrus had already looked back to him. Gaster frowned.

“Let’s go, Papyrus.” Papyrus didn’t move from the top of the stairs. Gaster’s browbone furrowed in something between irritation and confusion. “Come on, we have a number of tests lined up today. The sooner we get started, the sooner you can come home. I could pick up some dinner from that restaurant you like so much.”

And he actually sounded genuine. Sympathetic. Like he had sounded when he was trying to convince the boys that spending a long, boring day at the lab with him wouldn’t be _all_ that bad, and he would bring all sorts of nice toys for them to play with while they were there, and they would go somewhere fun the next day, really, he just needed to finish up this one project.

Papyrus wrung his hands and pressed his mouth into a tight line. He glanced down the hall, so fast that Sans almost missed it.

Then he took the first step down the stairs, and the tension in Gaster’s shoulders disappeared. He turned back toward the door and turned the knob.

“We'll see you tonight, Sans.”

Sans’s soul clenched and twisted. His body twitched, trying to reach out for Papyrus, still walking down the stairs, reach out to Gaster, even though he knew it wouldn’t do any good, knew it had _never_ done any good.

But now.

Now …

Papyrus was at the bottom of the stairs. The front door was open, and Gaster was taking his first step out the door, ready to lead Papyrus back to the lab for another day of hell.

“wait.”

Gaster stopped. He turned back toward Sans, his browbone furrowed, his expression so like it had been before that Sans could almost forget how much he had changed.

“Pardon?”

Sans swallowed and shook his head, back and forth, slow, desperate, lost. “don't … just ...”

Gaster waited, as if he might say something else, before he finally sighed, his shoulders falling in something like pity. It made Sans want to strangle him.

“Sans, we've been over this. I understand how much this upsets you, but I thought we'd come to an understanding. As soon as we get enough information to synthesize artificial human souls, we can—”

“there's a human upstairs.”

Sans didn’t realize he had started talking until the words were out of his mouth, hanging in the open air, shutting down every other sound in the room. He wasn’t even sure _what_ he had said until Gaster’s browbone furrowed again, further this time, and his full attention locked on Sans.

“I'm sorry?”

Papyrus was looking at him. Staring at him, his sockets so wide they almost didn’t look like _his_ eyes anymore, his mouth pressed into a tight, desperate line. His hands clasped together, trembling, and Sans could just make out a faint, pleading shake of his head.

Sans looked at his brother. His brother, the person he cared about more than anything in the world. The person who had endured more pain than Sans could imagine, and would keep on enduring it, until Gaster got what he wanted.

His gaze dropped to the floor.

“a … a human. papyrus found it. yesterday,” he said, the words burning as they slipped through his teeth. “it's in his room.”

Silence. Except for the almost-inaudible rattling of Papyrus’s bones, and the soft, irritated breath that left Gaster’s mouth.

“Sans, this is not something to joke about.”

“I’m not joking.” Sans’s head snapped up, his eyes hard, even as his soul twisted so hard it threatened to split. Before he could make out Papyrus’s expression, he looked up the stairs, toward the doors barely visible on the second floor, then back to Gaster again. “go see for yourself.”

Gaster stared at him, his eyes shifting toward the staircase. At last, he began to turn, taking his first step toward the bottom step.

Papyrus threw his arms out, blocking the way, his arms shaking so hard Sans could hear the bones rattling from across the room.

“No!” he shouted, his voice catching in his throat. “No, you can’t take her!”

That was all Gaster needed.

He moved faster now, until he stood right in front of Papyrus, and even though they were less than an inch apart, he seemed to tower over him, his eyes wide with eager anticipation.

“You found a human?”

A faint whimper slipped past Papyrus’s teeth, but as Gaster reached a hand up from his waist, the magic already beginning to gather around his fingers, Papyrus stiffened further, his arms spread out as wide as they would go.

“Stop! T-there’s nothing up there! My room’s very messy, I don’t want you to see it!”

Gaster’s magic curled around his soul and tugged, and he stumbled to the side, putting a hand to the wall to keep himself standing. He spun around, but Gaster was already halfway up the stairs, his eyes locked on Papyrus’s bedroom door.

“no! No, you can’t!” Papyrus cried, racing after him, but froze when Gaster gripped his soul, holding him in place. He struggled, kicking his legs, reaching out his arms toward the bedroom as his eyes widened further. “don’t hurt her! please don’t hurt her!”

If Gaster had even heard him, he gave no sign.

He threw open the door to Papyrus’s room and strode inside, his hold on Papyrus loosening, but not enough for Papyrus to run after him. Sans could move. He could have run upstairs, he could have said something, he could have _done something,_ but all he could do was stand there while his brother’s cries mixed with another’s. Higher-pitched, louder, shrieks of fear, of anger, of desperation, filling his skull until he thought it might burst.

Gaster reemerged, one hand still held out to keep Papyrus in place, the other angled behind him. And just as he stepped out of the room, the human followed, floating several inches above the ground, kicking and screaming, tears streaming down its freckled face.

It wasn’t until he heard the faint, marveled laugh that Sans turned his attention back to Gaster, and saw the awe practically glowing in his eyes.

“You really found one,” he murmured, just long enough for Sans to make out, turning his attention to Sans, such _pride_ in his voice that a tiny traitorous part of Sans wanted to blush. Gaster chuckled again, shaking his head and watching the human like he had watched the piece of Sans’s severed soul, even as it struggled and thrashed. “After all these years ...”

“Please!” Papyrus screamed, snapping Sans’s attention back to him. As Gaster started toward the stairs, toward him, Papyrus reached out, as if he could grab the human’s hand when it approached. As if Gaster would let him. “just take me, like you were going to. leave her there, you can do whatever you want to me! Please, Dad!”

Gaster wouldn’t look at him. For a second, Sans saw his face tense, as if holding something back, but a second later it smoothed out again, and he kept walking. One of his hands tightened around Papyrus’s soul and nudged him to the side, firmly, but gently enough not to risk him hitting the wall. As he approached, Papyrus struggled harder.

When they came within a few feet of each other, the human’s attention locked on Papyrus, and she stretched her arms out toward him, scrambling to grab his hand.

And just as Gaster slipped around Papyrus, out of his reach, one of Papyrus’s arms shot out to the side.

“ _No!”_

A flurry of bones materialized in the air in front of the door, and shot forward.

Right toward Gaster.

Gaster jerked out of the way at the last second, and the bones embedded themselves into the wall. Everything froze. Papyrus, Gaster, even the struggling little human still in Gaster’s hold, despite the shock. Gaster stared, first at the bones in the wall, then at Papyrus. Sans waited for Papyrus to fire another shot, to take advantage of Gaster being caught off guard.

But Papyrus just stared back, as stunned as Gaster, flicking his eyes to the bones as if he couldn’t believe that his own magic had made them.

If Gaster’s grip on him had loosened, he didn’t move to escape it.

And a few seconds later, Gaster’s hand curled a bit tighter, grip firm, as he looked away and sighed.

“Papyrus, stop this,” he said, with the same tone that he might have used if Papyrus had started flinging food around the house as a ten-year-old—even though Papyrus hadn’t so much as spilled food since he was two. “You know as well as anyone that humans are dangerous. They're our enemies, they're the ones who put us down here in the first place.”

“but this one didn’t do anything!” Papyrus all but cried, looking at the human with such affection, such pain, such fear, that it hurt for Sans to look at. “she’s small and she’s not even very old! she said she didn’t know anything about monsters before she came here!”

The human whimpered and squirmed, reaching toward Papyrus again, even though Gaster had now pulled her well out of reach.

“Nevertheless,” he said.

And without another word, he walked the rest of the way to the front door and pulled it open.

“Sans,” he called over his shoulder, without raising his voice. “Come on. I’ll need your help to get it to the lab.”

Sans’s breath caught in his throat. He choked, silent, frozen, as his eyes shifted back to his brother, just as the glow in his chest faded and Gaster’s grip on him disappeared.

Papyrus wasn’t stupid, no matter what anyone said. He knew when he couldn’t fight back. He knew that he _wouldn’t_ fight back. He looked at the human who reached out for him, he looked at Gaster who wouldn’t even turn around to meet his eyes, he stared and he tried to talk and nothing came out and his whole body shook with every second that passed and it became clear, _so clear,_ that there was nothing he could do.

Sans started to say his brother’s name, started to call out for him, started to say something, _anything,_ even if he had no idea what it was supposed to be.

Then Papyrus looked at him. Just looked at him, without saying a word, his mouth pressed into a thin, trembling line, his sockets wide and pained and gleaming with unshed tears, a faint glow in the backs of his sockets.

And before Sans could get out a single syllable, he turned and ran up the stairs, down the hall and into his room, slamming the door so hard that the house rattled with it.

Sans stood there. Motionless. Staring. The words still in the back of his throat, ready to come out, even if they never would.

“Sans.”

It was quiet, and more patient than Sans would have expected. But it was not the sort of thing that could be said twice.

Sans could have said no. He could have refused. He could have run upstairs after his brother, he could have tried to fight back against Gaster even though he knew he would fail, he could have just stood there and not taken a single step in any direction, he could have done any number of things that he would have been proud of.

Instead, he turned and followed Gaster out the front door, pulling it shut behind him. And without a word, he trailed behind Gaster and the newly-flailing, crying human, toward the lab.

It wasn’t that early in the morning. People were already awake, out of their houses, they must have passed twenty on their way to the lab. And every one of them saw what they were doing, everyone saw what was _with_ them.

She made sure of that, with every struggle and every scream.

But all Gaster had to do was say that they had found a human before every monster nodded and scurried away, some distressed, some intrigued, some excited.

No one tried to stop them.

The most they got was an offer of help to get the human the rest of the way to the king.

Sans wasn’t sure how Gaster managed to swipe his key card without dropping the human. He found himself wondering if he had always been able to use magic like this. Sans had never seen it. His dad had hardly ever used magic around them growing up, only to heal them and to grab their souls if they were in immediate danger. He didn’t like to grab their souls unless it was some kind of emergency. He had once mentioned that it felt like he was stealing their autonomy.

He wondered what Gaster would say if he reminded him of that now.

The elevator was the first obvious challenge Gaster seemed to reach. There was plenty of room for several people—a whole group of people, actually—but one squirming human held far enough away from them so she couldn’t reach them meant that she could easily kick the walls. The elevator was sturdy, and she couldn’t get to the buttons, but Gaster struggled to get her in and out without her grabbing onto the doorframe, and Sans wasn’t sure whether he hoped that she would be able to break free.

She never did.

Dr. Lemming was the only one in the underground labs this early in the morning. Sans had forgotten about them at first. He didn’t know how many weeks it had been since he had seen them.

But when he looked up on the way down the halls, there they were, ten or so yards away, watching them with wide eyes and an open mouth, as if they had something to say, but couldn’t figure out what it was.

Maybe that state was contagious.

Sans waited for them to protest. For them to do anything. But they just looked at the human, and Gaster, and Sans. Slowly, their shoulders fell, and their mouth twisted into a tight line. They gave a slow, curt nod, then turned away and walked down the hall.

Sans’s mind was far too dead to figure out what he was supposed to feel.

It was only in passing that he wondered whether Papyrus would have called them out on their inaction.

They stepped into the lab, and Sans let the door fall shut behind them. The human kicked harder now—was she smart enough to realize what was going to happen? Did humans have labs? Did they do the same kinds of things in labs?—waving her arms as hard as she could, as if she had a chance of whacking Gaster in the face and making him drop her.

“Stop it! Let go of me, _stop it_!”

Her voice seemed clearer now. Maybe since her voice echoed more clearly in the silence of the lab, or maybe there just weren’t as many distractions for Sans’s muddled head to focus on. Sans wished he could go deaf. If his lack of response was anything to go by, Gaster already had.

He had always responded to screams when they were kids. Always. Even if they were shrieks of joy. Even if it was some other kid, so far away he could barely hear it.

But now he ignored it with an ease that suggested he had already gotten used to it.

With Papyrus? Or …

Sans didn’t notice the chair in front of him until he walked right into it, tripping over the leg and almost crashing face-first into the floor.

Gaster tensed and turned. Sans steadied himself. And Gaster’s hold on the human loosened just enough for her feet to touch the ground.

She spun to face them, reaching to her belt and pulling something black from her right hip.

L-shaped, with one longer side, which she yanked up to aim right toward them.

Sans froze, just as Gaster turned to look at her again.

That was a gun.

He hadn’t even noticed it on her waist. He barely recognized it now. It wasn’t like he had ever seen a real one in the Underground, but he had read about them, in human books he had found in the dump or seen in the library. Weapons. Human weapons, far more destructive than anything the humans had had access to during the war.

Lethal to humans.

Which meant they would be even more lethal to monsters.

She pointed the gun at Gaster, then at Sans, then back at Gaster, holding it on him even as her hands trembled so hard they threatened to drop it. She swallowed several times.

“I’ll … I’ll do it!” she managed, her voice shaking just as hard as the rest of her. She gripped the gun tighter, though she didn’t seem to know what she was doing with it. “I’ll shoot you! Don’t get any closer! Just l-let me go and I won’t … h-hurt you …”

She took a step back, careful, uncertain. There was no way she could make it back to the door without looking over her shoulder. Sans didn’t move, and at first, neither did Gaster, but while Sans had begun to sweat, Gaster just looked at her, his face blank, his eyes cold and calculating.

Then, in such a quick, fluid motion Sans could barely make it out, he gripped her soul, yanked her toward him, and snatched the gun right out of her shivering hands.

He kept his hold on her as she shrieked and cried and struggled, his free hand holding the gun and looking it over. He didn’t seem to have any more idea of how to use it as Sans did, but finally, he put his hand on what Sans was fairly sure was called the trigger, pointed it at the opposite wall, and pulled it.

Sans flinched.

Nothing happened.

Gaster stared at the gun, then tossed it to the side, where it clattered to the floor.

“Empty,” he muttered, with a tone Sans could only describe as unimpressed.

Without another word, he picked up the human by her soul and dragged her, kicking and sobbing, across the room, toward the examination table. He lifted her up and shoved her back down on it, holding her there as he strapped her down. Sans’s soul clenched with every strap that clicked into place, the same straps that had held him to that same table, the same straps that had held Papyrus.

“Sans, get it hooked up to the monitors,” Gaster said as he finished, stepping away from the table and giving Sans a glance that lasted less than a second. “I’ll need a few minutes to get everything set up, but I want to get started right away.”

Sans just stood there. Why couldn’t he move? Why couldn’t he refuse to do this, why couldn’t he get up and leave, would it make any difference if he did nothing? Gaster wouldn’t go back to using Papyrus just because Sans wouldn’t help him with the human, would he?

But Sans found his feet moving anyway, carrying him across the room, toward the monitoring machine that had been hooked up to his own bones more times than he cared to count. He lifted the wires and pulled them up to the human, adjusting their shirt to put the electrodes in what he could only guess were the right places.

She was still crying.

“Please … m-my name’s Rachel … I … I don’t wanna hurt anyone, I just wanna get out of here, your … your brother, that was your brother, right? Papyrus?” she asked, her voice barely more than a whisper, a whimper, the tears streaming down her cheeks so hard they dripped onto the table below. Sans said nothing, but his hands slowed. The human shifted. “He s-said m-maybe if I made it to the castle, the king would help me. I just wanna go home, please, I just wanna go home.”

Sans paused. His hands tightened around the wires he had yet to hook up to her chest. She was watching him, even though he didn’t meet her eyes.

She didn’t look all that strong. She didn’t look dangerous.

She looked … squishy. Soft. Fragile.

The electrodes on her pale skin looked even worse than they had on his own bone.

The sound of Gaster bustling around behind him filled the air, and Sans gritted his teeth, added the last of the electrodes, and walked away.

“Don’t! Stop! Don’t hurt me, please don’t hurt me, no, let me _go_!”

She sounded young. Like Papyrus. Younger than Papyrus. Young and confused and afraid.

This wasn’t what humans were supposed to be like. They weren’t supposed to be small. They weren’t supposed to be weak. They weren’t supposed to be scared. And they weren’t supposed to be kids.

As Gaster approached her, her words devolved into mindless screams of panic, her arms and legs flailing under the restrains. She kicked and struggled but the straps never gave in. Even when Sans nearly put his hands to the sides of his head to muffle the sound, Gaster never even flinched.

He looked her over, like he might look over a machine when trying to figure out whether it would be useful in an experiment. Or the way he had looked at the experiments themselves. The icy bracelets, maybe, or readings for the Core.

Was that how he had looked at Sans and Papyrus, when they were in those tubes?

“Yes, it should be a good starting point. I never did get a baseline for humans for that,” he muttered, more to himself, even though he spoke loud enough for Sans to hear him. “Sans, there should be a scalpel in that drawer to your left. Could you bring that here, please?”

Sans’s legs moved before he could think otherwise. He didn’t need to be told where the scalpel was. He had seen Gaster take it out enough times to have it memorized. Apparently he hadn’t changed its home since then.

He carried it back across the room with numb limbs, and when he stopped at Gaster’s side, Gaster actually turned to face him before he took it in his own hand.

“Thank you.”

Sans was ready to turn around and go back to … just to walk away, but a hand touched his shoulder before he could move. Sans stiffened.

“Thank you for telling me,” Gaster said, more quietly, more gently, with a voice Sans could almost believe sounded just like his dad’s. He paused for a moment. “I hope I can count on your continued help throughout these tests?”

The human was still screaming. Sobbing. Crying out for someone to help her, anyone to help her.

Gaster looked at him as if he couldn’t hear a sound.

Sans said nothing. But he didn’t say no.

Gaster let go of his shoulder and turned to the human once again. He lifted a hand, curled his fingers, and pulled up.

A yellow heart fazed through her chest and floated in the air just above her body.

For a moment, she stared. Then she thrashed harder.

“No! _No!_ ”

She had seen her soul before. Was that normal for humans? Or had she already had a chance to see it since she fell into the Underground?

Had it been a fight she had started?

Or …?

Gaster gripped her soul in one hand, more roughly than he had gripped Sans’s soul, even in the worst of the experiments, even when he didn’t seem to realize what he was doing, when he still would have _stopped._ She flinched. She whimpered. She stared up at him, sobbing out words Sans couldn’t understand. Gaster didn’t hear it.

He lifted the scalpel to the bright yellow soul, and Sans couldn’t even bring himself to close his eyes.


	32. -10

**Notes for the Chapter:**

> No humans tortured in this chapter! Can't say much for next chapter, though ... (I'm so sorry.)

He was going to be late for the science fair.

He had promised he wouldn’t be late for the science fair.

He had been sure, absolutely _sure,_ that he had set the alarm on his phone to go off five minutes before he had to leave the lab, so he would have a bit of extra time to finish up any work he had going and hang up his coat before he left. And he _did_ set the alarm. The problem was that, no matter how loud the alarm was, very few things could snap him out of his thoughts when he was in the middle of something this crucial.

Which was why he was now sprinting through the Capital toward the boys’ school, so fast his legs and chest ached, a good twenty minutes after he had planned to leave.

He couldn’t remember the last time he had run this fast, and he wasn’t sure if he had ever run this fast over so long a distance. He definitely wasn’t in shape for it. But as the school came into sight, he picked up his pace further, panting hard enough to make him almost believe he had grown a pair of lungs.

It was more crowded than he remembered it. It always was at special events, and the annual science fair, from what he had heard from parents of older children, was a _very_ special event. He nodded in greeting to some of the other adults he passed as he stepped through the front doors and made his way down the hall, searching out the cafeteria which had been taken over for the students to set out their projects.

If the halls had been packed, the cafeteria was overflowing. It wasn’t a particularly large cafeteria, but then again, nothing was very large down here, and it was big enough to fit the entire school at lunchtime, but now, with a significant portion of the student body, teachers, and parents and extended family all crowded in, it looked like it might burst at the seams if only a few more people walked in.

And there were still more people in the hall behind him.

Once, Gaster might be balked at going into a space like this—there was a reason he preferred to work alone in the lab—but this was his son’s first science fair, and no crowd was going to stop him from being here for it.

So he stepped inside, muttering apologies no one understood when he had to push past several other people just to get a few feet in. But everyone knew him, and everyone—apparently—liked him, or at least liked his sons, so they had no problem letting him through. For once, he was actually grateful for being taller than most people around him, so he hardly even needed to strain his neck to peer around at the tables and projects that had been set up, some scattered near the middle, some along the walls to his side, and even more pressed against the wall in the bac—

There.

He hadn’t been told where they would be setting up—he wasn’t even sure they had known before today—but it wasn’t hard to spot them, even though they were two of the shortest people in the entire room. They weren’t exactly a lot of skeleton monsters around, and Alphys, as much as she tried not to draw attention to herself, still managed to stand out in a crowded room with her bright yellow skin.

Gaster navigated the crowd with a skill developed over years of school events, and in under a minute, slipped past the last few people to reach the table. It took Sans a few seconds to notice him, but once he did, he immediately turned away from the folded posterboard they had set up behind the contraption on the table to flash him a wide grin. Alphys blinked, then followed his gaze. She jumped.

“Oh! H-hi, Dr. Gaster!”

Even after all these years, she still looked at him like she might look at a celebrity. He had tried to rid of her that notion years ago, but at this point, he was beginning to doubt he would ever succeed. Still, he gave her a smile and lifted his hands.

HELLO ALPHYS. HOW YOU?

“I-I’m good … just h-helping S-Sans finish s-setting up here,” she replied, glancing back at the table. “N-not that he needs m-much help …”

Sans snorted and waved her off. “She’s just being modest again. I never would have been able to set this whole thing up so fast without her help!”

Alphys’s cheeks went red, and she glanced away, only reaching back to nudge Sans in the shoulder before holding her arms close to her chest.

“You f-flatterer …”

Still, she couldn’t quite hide her smile. Gaster felt his face softening as he looked between her and Sans and watched them go back to work, trading instructions and dividing up final tasks without even needing to say a word.

When he had first met Alphys, he would have never expected that she would stick around for as long as she had—and he definitely hadn’t expected she and Sans to become friends. They were five years apart, after all, and they had met when she was ten and Sans was only five. She got along well with both boys, of course, but though she was kind to Papyrus, she was more like a big sister to him, while she was closer to a good friend for Sans, even if he was a good deal younger.

They enjoyed similar topics and even early on in her babysitting, could go on for hours at a time about anything related to math or science, so much so that Papyrus would often complain about being left out, and Alphys, being the kind soul she was, would make sure to spend some time playing board games or watching movies with him, despite how much fun she seemed to have chatting with Sans.

But the boys were older now, almost old enough to not need a babysitter for short outings. The neighbors—even though their house was a bit isolated from some of the others—kept a good eye on the boys when Gaster was out, just as they had since they were small. If Alphys had been just a babysitter, she probably would have started looking for other regular engagements to keep herself busy.

As it was, she spent just as much time at their house as ever, and her enthusiasm for talking with Sans only seemed to have grown since she learned she had been accepted to the university, starting in the fall, at fourteen years old.

It was a relief to have her around, and not just as someone to take care of his sons. She was one of the few people Sans could hold an in-depth conversation with on various scientific topics, one of the few people who was happy to teach him new things if she knew something he didn’t, but was also happy to accept that there were some things he had already picked up. Gaster had long suspected that Sans would get along better with older children, and Alphys had only proven that theory ten times over.

Especially given how little Sans interacted with his actual classmates nowadays …

“Is Pap coming?”

Gaster jumped at Sans’s voice, shocking him out of his thoughts. Alphys was still focused on adjusting the posterboard—though it seemed quite adjusted enough—but Sans stared up at him with wide, hopeful eyes. Gaster chuckled.

“Of course. I think he said he was going to try and catch the first part of art club, but I know he wouldn’t miss this for the world. I hope he didn’t get lost on the way here …”

He signed a few of the words on a habit he had been trying harder and harder to build up—it had become far too common to find people staring at him blankly whenever he spoke to his sons—and though he was sure it had been far from a complete sentence, Alphys, watching from over her shoulder, apparently caught the meaning. She straightened and offered a shy smile.

“I-I’ll go l-look for him! I know t-this school p-pretty well …”

Gaster thought about declining and insisting on searching for Papyrus himself—Alphys was really doing far too much of his parenting work already, given that she was no longer accepting payment—but she had already started back toward the front of the room, so he just smiled and nodded, lifting his hands in a quick THANK-YOU.

“Thanks, Alph!” Sans called out, and Alphys smiled and waved before slipping away, staying close to the walls to avoid the worst of the commotion.

Gaster chuckled, watching her go and wondering when she had grown up so fast. Perhaps she would never be his child, but she had been around long enough for him to consider her part of the family.

He would have to make sure to get her something good for her high school graduation next month.

As she disappeared, he turned back around to face Sans, who had already returned to his project. There wasn’t much left to do, apparently, but Gaster understood the need to look things over one more time before the “final presentation.” Perhaps he had never participated in any science fairs, but he was fairly sure that personal visits from the king had a similar effect—even if the king wasn’t a scientist and probably wouldn’t have understood even if Gaster had presented him with a literal piece of junk.

It would have been clear to anyone who looked at it for more than a second that what Sans had created was _not_ a piece of junk. Gaster doubted anyone would be able to tell what it _did_ —even he couldn’t tell that—but whatever it was, it was complex, it was intentional, and he had no doubt it was going to serve its purpose well. Whatever that purpose turned out to be.

It was about the size of a small box, a foot high and a foot wide, made of pieces of metal screwed together, a control panel up front with dozens of tiny lights and what he suspected was a good bit of wiring inside, based on the supplies Sans had carried up to his room a few weeks before. He had seen Sans working on it, even though he had tried to hide it as much as possible. Gaster respected both his sons’ privacy, but sometimes it was just a little too tempting on weekends when Sans left his door open and it was _oh so easy_ for Gaster to poke his head in as he passed by.

He had known, from the day the science fair was announced three months earlier, that Sans wasn’t going to do something as simple as a baking soda volcano, or even a “how color affects feelings” project, as three of his classmates had apparently seen fit to do. At first, he had expected that Sans would ask his advice, maybe even ask him to help out with making a complicated, interesting project, better than anything he could have found in a book of science fair projects. But he didn’t. He came home, announced the science fair, then immediately ran up to his room and closed the door to get to work.

If Gaster hadn’t known his son as well as he did, he might have been offended.

But as it was, he had just chuckled and shook his head fondly, then went to make dinner.

He _was_ a little sad when Sans began skipping their usual evening and weekend “family time” in order to work on his project. If nothing else, Gaster had hoped they could collaborate so they could spend more time together. He had been so busy lately—for the past few years, really—and he tried to spend every minute of his free time with his boys. But he supposed it only made sense. Sans had been doing almost everything related to school by himself—or with Alphys—for years now. He didn’t need Gaster’s help, and he had become independent enough not to want to ask for it.

It hurt, in a way. But at the same time, Gaster couldn’t help but feel a swell of pride that Sans had done all of this without his input.

Now, Sans stared at his finished creation with the biggest, proudest grin Gaster had seen on his face in years, if not ever. His eyes gleamed with pure joy, and Gaster felt his chest soften and warm even further. He considered taking out his phone and snapping a picture, but Sans was going through a phase where he preferred not to have goofy pictures taken—except for very special occasions—and though Gaster hoped he would allow a photo later, for now, he could just try to make sure he engraved this moment deep in his head.

“You never did tell me what you were building,” he said at last.

Sans turned to face him, blinking for a second before the words seemed to click. He looked down and shrugged, a smile tugging at the corners of his mouth.

“I thought I’d make it a surprise.”

“Is it time for the big reveal yet?” Gaster asked.

Sans looked up at him out of the corner of his eye, his smile twitching wider. “Can you guess?”

Gaster chuckled, but complied, stepping closer and peering down at the odd piece of machinery. For the first time, rather than simply being amazed by the complex device his _son_ had created, he allowed himself to think critically, examining each and every piece and trying to figure out what it could be used for.

Like just about everything down here, it had been built using pieces Sans had found in the garbage dump—with Alphys’s eager help, given that she liked to take him to the dump whenever it was just the two of them. But the metal used was particularly hardy, more heat-resistant than other metals might be. He probably expected it to be running a lot, very fast, or perhaps somewhere particularly hot. That narrowed it down a bit. It was relatively small, and contained a fairly complex control board, and he couldn’t think of something it could do by itself. Perhaps it was meant to be paired with something else? Perhaps as an addition to an existing machine?

“The wiring seems familiar … not exact, but I know I’ve seen this type of machine before,” he murmured, as much to himself as to Sans. He leaned a bit closer, browbone furrowed. “Or at least the ports. It reminds me of—”

He stopped.

The pieces clicked so fast he swore he could hear the snap as they fell into place.

Out of the corner of his eye, he watched Sans’s smile grow, just a bit, his cheeks flushed with a faint blue. Gaster turned to face him, blinking. Sans put his hands behind his back and fidgeted, his eyes glowing brighter than Gaster had seen them in years, his smile beaming yet just a little nervous, so much like Alphys it was almost scary.

“Do you get it yet?” he asked, his voice barely louder than a whisper. He glanced toward the machine, then to Gaster again. “It’s a temperature stabilization mechanism. For the Core.”

Gaster blinked. Then he blinked again. He looked to the machine, then back to Sans, the machine, Sans, again and again, his mouth hanging open like an idiot, his sockets so wide they hurt.

“A … you built … it’s a _what_?”

“A temperature stabilization mechanism,” Sans repeated, a little louder, his smile a little smaller. “For the Core.”

Gaster just stared. Again, he looked between the machine and Sans, trying to make the words register in his head.

“You … built something for the Core?”

“Uh-huh,” Sans replied, and though there was still a bit of pride in his voice, Gaster could see more anxiety creeping in with each second that passed. He rubbed the side of one foot with the toe of the other. “You … had a few extra copies of the blueprints lying around, and we go there often enough, so I kind of … looked to see where it could fit, and … made this.”

Gaster’s browbone furrowed. He looked down at his son—nine years old, he was still only _nine years old,_ wasn’t he?—whose gaze drifted up and down, from Gaster to the floor, his smile now settled into his neutral permanent grin. Gaster shook his head.

“Sans … you … I thought you’d just be making some sort of _machine,_ I didn’t think you …”

Sans’s shoulders hunched. He glanced behind Gaster, as if searching for Alphys, even though she had already long disappeared into the crowd. His eyelights dimmed.

“Do you … not like it?”

Gaster jerked his head toward him, blinking as his son’s expression sunk in. He blinked a few more times before shaking his head so empathically it almost hurt.

“Sans, I _love_ it,” he breathed. He turned to the machine again. “I … I just … this is _beyond_ anything I could have expected, I don’t even know what to say, I …”

A breathy laugh slipped past his teeth, and his mouth curled into a smile as Sans straightened again, his eyes bright and pleased. He looked like a toddler, his excitement unbridled, warm and rolling off him in waves. Gaster stared at him for a few seconds, taking in that face, memorizing every inch of it, just in case it took a while before he saw it again. Then he looked to the machine, huffing another disbelieving laugh.

“I didn’t know you even liked machinery.”

Sans didn’t stop grinning as he shrugged with one shoulder, slipping his hands into the pockets of his shorts.

“Well, I mean, it’s not my _favorite_ thing. But it’s still really cool, and I learned a lot doing this. And it’s useful! None of the other stuff I could think of would actually do any good.”

Gaster paused. He turned to Sans in full again, frowning. “I thought you were interested in learning about outer space?”

Sans glanced away, just for a second, just long enough for Gaster to catch the flash of an unidentified emotion that flew across his face. Then it was gone, and Sans looked back to him with a smile and another shrug.

“nah.”

He said it as if that should be all the answer he needed to give. But Gaster kept staring at him, and after a few seconds, Sans looked down, fidgeting, shoving his hands a little further into his pockets.

“I mean … that was cool when I was little, but … I know I’m never gonna actually see it,” he went on. A tiny crease formed in the center of his browbone, and just as before, Gaster couldn’t figure out what it meant. “I’d have to be on the surface to even see it through a telescope, and there’s no way I’d actually get the chance to go up there.”

Something deep in Gaster’s chest twisted, pinching his soul until he almost forgot how to breathe. Then Sans’s head snapped up, and he smiled again, wide and almost genuine enough for Gaster to believe.

Desperate. Reassuring.

He was _nine._

“But that’s okay!” he finished, and Gaster would have bought it, if he hadn’t seen the look on his face seconds before. His shoulders relaxed where they had tensed up. “There’s all this other great stuff I can learn right here. Alphys leant me this really good physics textbook that she found in the dump, and some of the pages are ripped out and others have a lot of scribbles in them, but most of them are still good! She said she could help me learn more about it if I wanted.”

Gaster looked at him. Just looked at him, for a good half minute. And Sans looked back, unwavering.

He shouldn’t let this go. He shouldn’t just accept this. He shouldn’t let himself forget, even for a second, that look on his son’s face. That look like he had watched something he had always hoped for drift away, but had known that there was no point mourning it, so he had simply moved on.

But as Sans smiled up at him, so genuine, so _real_ —even if it wasn’t—he still forced himself to smile back.

“Well. You shouldn’t have any trouble with that,” he replied. And Sans’s answering, wider grin was almost enough to convince him he had made the right choice. He shifted. “I am … I really can’t express how proud I am of you for doing this.”

“It wasn’t that hard,” Sans said with another shrug.

“I know you’ve been staying up late working on it,” Gaster countered.

Sans’s cheeks flushed, but he was still smiling, and this time Gaster actually believed it.

He looked back up, meeting Gaster’s eyes with his own wide eyelights, eager, expectant, hopeful. “Do you think you’ll be able to use it?”

Gaster grinned down at him, and it wasn’t even hard.

“This will make things much easier for me,” he said, allowing himself one more glance at the machine, taking in all the details and trying to imagine how much work Sans had put into it. He shook his head. “I’m not even sure if I could have come up with something like this, to be honest with you.”

Sans snorted, waving him off even more enthusiastically than he had done with Alphys.

“Oh, come on, Dad! You could have built this thing in your sleep!”

“I sincerely doubt that,” Gaster replied.

Sans started to say something, then stopped and simply stared at the ground again, his face even bluer than before. Gaster reached out and touched his shoulder, giving it a quick, gentle squeeze.

“Do you have anything else to finish up here? I think they’re getting ready to start soon,” he went on, nodding toward the table. He paused and chuckled. “Not that there’s any competition, but they’ll at least want to throw the other kids a _bone_ and look at their projects first.”

Sans either hadn’t hear or didn’t care about the pun, because his head snapped up right away, his body straightening so fast he almost knocked Gaster’s hand off his shoulder.

“Oh! Right!”

Then he was back at the table, looking over the machine one final time, twisting the knobs on the control panel and pressing several of the buttons, watching the tiny lights he had installed in the front glow in what was, based on his expression, the way they were supposed to.

He looked so natural, doing this, even if he had never worked with machinery before. He had dived into this, soaked it all in, just like he had so many things that had caught his interest over the years. He _was_ interested in this, Gaster could tell. He wasn’t lying about that. But it hadn’t been what he dreamed of. It hadn’t been what had completely enraptured him from the age of four, when he had first seen a photo in a human book of the night sky. It hadn’t been what he had been so determined to study for the rest of his life.

When had he given up?

When had he decided that his dream, which had consumed hours, days, _weeks_ of his time when he was younger, wasn’t even worth pursuing?

Yes, Gaster had always known it would never come true. He had known that one day, if Sans never gave it up, he would have to explain to him that there was a limit to how much he could learn in astronomy. Shouldn’t he be grateful that Sans learned it on his own? He didn’t have to go through that. He didn’t have to crush his son’s dreams. And even better, Sans didn’t even seem terribly _crushed_ by the realization. Disappointed, and a little sad, but … he was moving on to other things.

But it still hurt.

This was his son. His “budding little astronaut,” as he had called him once before Sans decided the name was embarrassing and asked him not to use it in public. Even if he had something else to be passionate about, it wasn’t any less of a loss to watch one of his more treasured dreams fade away.

Was it as much of a loss for Sans as it was for Gaster?

Or … was Sans okay with this?

He could finally do something practical with his knowledge, after all. It wasn’t just reading textbooks, it was doing something, _making_ something. He had always wanted to help. Always wanted to do something important.

And this gave him that chance, didn’t it?

Even if it hurt.

Even if it meant losing something that had once been so important to him.

Even if it meant Gaster accepting that his son was no longer quite as little as he once had been.

“Sans! The judges are coming! Get ready!”

Both of their heads snapped up at Alphys’s voice, rising above the chatter of all the other people in the room. Sans looked at Gaster, and Gaster looked back. As Alphys neared them, Sans was already positioning himself just in front of the table, facing forward, ramrod straight, his best presentation-face on even as his hands fiddled in front of him.

Gaster’s chest still ached, but he couldn’t help the smile that turned up his mouth.

He had hoped, hoped so badly, that Sans wouldn’t grow up this fast. That he would hold onto his dreams even if they would never happen. That he would reach for the stars, even if he would never be able to touch them.

If there was one part of parenthood that he hadn’t expected, it was the ache of watching his children grow up.

But if life had to take away his first passion, at least it had given him something else to fill the void.

And behind the nervous, stiff posture Sans held for the judges, the gleam of excitement in his eyes was real.

Alphys finally stumbled out of the crowd to stand at their sides, and a second later, a small, thin skeleton, already several inches taller than her, followed, running to pull Sans into a hug before stepping off to the side to give him room. Papyrus looked up at Gaster with a proud grin, which Gaster returned without hesitation.

Sans would be alright.

Maybe he had to give up one of his dreams, but he had plenty more he could still pursue. And, from what Gaster could see, he would pursue them as far as he could.

And no matter what he ended up doing, Gaster had no doubt Sans would blow them all away.


	33. Chapter 27

**Notes for the Chapter:**

> I haven't said it for a while, but to everyone who has left kudos, bookmarked this story, commented on it, or just read it, thank you. You guys are amazing. :)
> 
> By the way, those tags on the top of the page? Read them before you read this chapter. Seriously. That's ... going to apply to a lot of the chapters from here on out, actually.

It was the longest day of Sans’s life.

And Sans had had some very long days to compare it to.

He never watched the clock. He would have gone crazy if he had focused on the ticking of the hands, and besides, there was no guarantee that Gaster would stop when the normal workday ended. He had stayed late plenty of times when he was in the midst of an important project before, and that had been _before,_ back when he still put a certain amount of priority on other things in his life.

With Papyrus, it wasn’t uncommon for him to stay late in the evenings, if only because then, there was no one in the building to hear the screams.

This was a weekend. There was no one else in the lab to hear them.

And Gaster took advantage of every second.

Sans didn’t know why he stayed the whole time. He could have left. There was no threat hanging over his head, Gaster had never even explicitly told him to stay. But every time he started to step toward the door, Gaster would give him another instruction, and Sans would find himself obeying almost without thought.

He didn’t like to think about it.

Night had already fallen by the time the experiments wound down and Sans finally left the lab, riding the elevator up and trudging through the ground floor and back outside. The human was asleep—or unconscious, was there a difference?—and Gaster had taken to sitting at his desk, compiling all the notes he had taken throughout the day. In any case, he didn’t ask for Sans’s help, and he didn’t protest when Sans stepped through the lab door. Sans wouldn’t have been surprised if he was there half the night.

He wasn’t sure whether he wanted him to be.

He walked slower than usual. He couldn’t decide whether he wanted to go back to the house. Sometimes the thought of home would overwhelm him and he would want to run the rest of the way there, but other times he actually considered going to Waterfall and sleeping in his lab for the night.

But eventually, he found himself back on his own front porch, and he spent a minute staring at the doorknob before he finally turned it—unlocked, just as they had left it this morning—and opened the door.

It took several seconds for his eyes to fall on Papyrus. Even though he was still dressed in his favorite brightly-colored sweater, he seemed to blend into the corner of the couch, curled up into a tiny ball Sans could barely recognize as his brother. He looked up, dark lines on his cheekbones, like the remnants of old tears. Sans stepped inside and pushed the door shut behind him.

Something deep in his core relaxed, then twisted again.

“hey, pap.”

Papyrus didn’t reply. He looked at him, his face just as unreadable as Gaster’s had been. His mouth pressed together, his sockets wide, a tiny crease in his browbone, like something was hurting him but he didn’t want to say what it was.

Sans winced and shook his head. “pap, i … i’m …”

Before he could continue, Papyrus threw himself off the couch and crossed the room so fast Sans barely saw him move. He ran up the stairs and down the hall, his face pinched, his eyes aimed resolutely forward.

“papyrus!” Sans called after him.

He swore he saw a hint of fresh tears in his brother’s eyesockets in the second before he slipped into his room and shut the door behind him.

It wasn’t quite a slam. Papyrus didn’t slam doors. But it left Sans feeling like he had been slapped across the face.

He tried to call his name again, but the sounds stuck in his throat. He stood there, trying to force the words, but finally gave in and let his arms fall to his sides.

Sans could just make out the faint click of the lock from inside the bedroom.

Papyrus had never locked his door.

Sans stood there for at least five minutes, just staring up the stairs. He didn’t know what he was waiting for. Papyrus wouldn’t come back out, and Sans knew that. He thought he knew that. He _should_ know that. But he kept waiting, as if Papyrus might throw open his door and run down the stairs and pick him up and hold him and tell him everything was going to be alright.

Then Sans would cry and cling to him and they would just stand there, sobbing, before they figured out a way to solve this.

Papyrus didn’t come.

Sans dropped his bag on the floor, not bothering to put it away. Papyrus had always been the one to remind him to do so. He walked up the stairs, and it felt like trekking across the entire Underground for the ache in his legs. How long had he been standing that day? Had standing always felt so exhausting?

He wanted to sleep. He wanted to close his eyes and go to sleep and never wake up. That sounded nice. Never waking up. Never going back to the lab.

He collapsed into his bed face-first, not bothering to change his clothes or even kick off his shoes. He had thought that as soon as his body hit the mattress, he would fall asleep, but even though his sockets shut right away, sleep didn’t come. He thought about getting up to turn off the lights, but his legs wouldn’t move. His body refused to budge, yet it refused sleep even harder.

His bed wasn’t as comfortable as it had been before. It was stiff and dusty. Before last night, how long had it been since he had slept in it? Papyrus’s bed felt much softer than this.

Warmer. Safer.

Less alone.

But he couldn’t go to Papyrus’s bed anymore. He had lost that right. He had given it up. So he stayed here.

He wasn’t sure if he slept. He spent most of the night slipping back and forth between something like wake and something like sleep, like a vague dream, where his thoughts were muddled but not quite strange enough for him to be sure he was sleeping. He spent more than an hour awake, staring at the ceiling, before he got up in the morning.

He kept hoping that he would hear the clatter of dishes downstairs. But he never heard a sound.

Gaster’s door was still closed, and Sans could hear nothing from inside. He almost checked Papyrus’s, but paused before he could get within two feet of the door. He clenched his teeth and passed it.

It didn’t feel right to listen.

Even if he already knew what he would hear.

He didn’t feel like eating. He was hungry, probably. At least he had the physical sensation of hunger. But every time he looked at food, he only felt worse. And it felt good being hungry, in a way. Papyrus would have nagged him to eat, if he had been there. But Papyrus wasn’t there. He didn’t want to be there. He didn’t want to be around Sans.

It was silly, even to his own head, but feeling the pangs of hunger somehow felt like he was making up for his sins.

Except without the whole “making up for them” part.

He was halfway to the lab before he realized that he could have stayed home. Gaster had never told him to come back tomorrow. He could have lounged on the couch all day, and it might not have changed a damn thing.

But that was just it. It didn’t matter what he did. He couldn’t change a _damn thing_.

Or maybe he could.

But he wasn’t going to.

Dr. Lemming must have been at the lab by the time he arrived, given how much of an early riser they were. But Sans didn’t run into them. The lab felt empty. Dead. Had it really looked like this a few months ago? Had this been the same place he had eagerly rushed to on his first day, hoping to spend hours working on something important? Something meaningful? Something life-changing?

He didn’t knock when he opened the door to Gaster’s lab, and Gaster didn’t notice when he walked in. He was standing across the room, making notes on a sheet of paper on his desk. Sans couldn’t tell whether or not he had gone home, or even slept. He looked exactly the same as he had the day before.

The human still lay on the same examination table. She wasn’t moving, and Sans had to stare for a good ten seconds to be sure she was even breathing.

He stood there for more than a minute before Gaster lifted his head, blinking, but not tremendously surprised. He gave a small nod before turning back to his own papers.

“Good, you’re here. We should be ready to start today.”

It took a few seconds for the words to click in Sans’s head. Maybe he had misheard. Maybe he was tired enough to hear things. But the longer he looked at Gaster, the clearer it became that he had heard every word right. His browbone furrowed.

“i thought you already started,” he said, his voice cracked with disuse. “yesterday.”

“The preliminaries, yes,” Gaster muttered, without turning to face him, bustling around a machine by the wall. “I had a few blanks I needed to fill in from my previous research. The tests with you and your brother showed me exactly how disorganized I was with my original experiments, and I had a few baselines that still needed to be taken.”

“baselines,” Sans repeated.

“Yes. Baselines.” Gaster paused and glanced over his shoulder, just long enough to meet Sans’s eyes, before they returned to the machine. “They may not be useful, but I wanted to get them over with in case the extractions affect the human’s physical state.”

“… extractions?”

For the first time, Sans noticed exactly which machine Gaster was hovering near. He had seen it before. He had seen it a thousand times, it had been there his whole life, gathering dust, he had studied it during his first days here, he had tripped over its cords and knocked himself out and scared his dad half to death.

It looked different than the others. Oddly-shaped. Like a … skull, but not a regular skeleton skull. Like a skull with pinchers instead of a mouth, large and foreboding and it had been there all these years, why did it look so different just because the dust had been wiped clean?

How long had it been since it was used?

How long had it been since it was even _touched_?

His dad had built it. And just like every other machine in this lab, Sans knew what it did.

He had just never thought about the fact that once, decades ago, it had actually been _used_.

“Up until now, all S.E. has been extracted from the souls of dead humans,” Gaster said, his attention on the machine rather than Sans. He ran a hand over the metal side, his gaze distant, as if thinking back. “I didn’t think to extract any from a living human, even when I had one readily available.”

“what are you getting at?” Sans asked, even though he knew, he wasn’t that stupid, he _knew._

Gaster glanced at him again, a little longer this time, though he didn’t seem to really be seeing him, any more than he saw the human lying on the table.

“After dying, human souls retain all the same attributes as they did during life,” he started, and Sans bit back the impulse to tell him that he _knew_ all this, he had taken virtually every science class they offered at college, and he had read all the files Gaster had on the last human soul. Gaster paused. “However … they are unable to recreate those attributes. What is extracted from those souls cannot be replaced. The human has died, and the soul cannot replenish itself. That is why I was so careful with my extractions from souls in the past, and why I couldn’t procure any new S.E. after I used the last of it on Papyrus.”

His eyes drifted away, back toward the machine, then again toward the human lying on the table.

“But a living human …”

Sans’s breath caught in his throat before he forced it through. Gaster’s face tensed, just for a second, when he looked at the human, before that intrigue lit it up once more.

“A living human can replenish whatever is taken away, as long as it is done carefully. With a living human … I can get as much as I need,” he went on. “Enough to synthesize another human soul.”

He turned back to Sans, and it took Sans had not to look away.

“This human makes six, Sans. We only need to synthesize one.”

Sans had known that. He had thought about that, those were the same thoughts that were running through his head when Papyrus brought the human home in the first place, but he hadn’t _really_ thought—

Gaster said nothing else. And Sans just stood there and watched while he dragged over some of the cords from the machine by the wall—the same machine Sans had almost killed himself tripping over—and began attaching some of the smaller ones to the human. It looked a lot like hooking her up to a monitor. But this wasn’t a monitor. It was …

Sans had never seen it work before. He had no idea _how_ it worked. He had studied it, just like he had studied all the other machines in the lab, but he had no idea what to do with it. It hadn’t been relevant to his research. It hadn’t seemed relevant to anything.

The human squirmed as Gaster replaced the cords hooked up to her with new ones. Sans couldn’t tell whether she was really awake, but she tried to jerk away from the unfamiliar touch. But the straps held her in place, and Gaster didn’t even seem to notice her discomfort.

Sans tried to imagine being strapped down to a table when he was a kid. He tried to imagine having his clothes pulled up and down and the machines hooked up to him and squirming and crying and screaming and no one listening.

All it had taken was a whimper for his dad to listen to him when he was a kid.

She finally opened her eyes when Gaster walked away, back to the machine. She scanned the room, as if she wasn’t quite sure where she was, or what was going on. Maybe she had forgotten. Maybe she thought it was just a bad dream.

She tried to move her arms and legs, and jerked her head up when she found they wouldn’t move. She still looked tired. Too tired to react as strongly as she had the day before. Soul experiments, even if they hadn’t been soul- _cutting_ experiments, seemed to have the same effect on humans as it did on monsters—or, at least, on Sans. But the sight of herself strapped down to the table jolted her awake, and she began to struggle once again, staring at the cords hooked up to her, her eyes shooting from side to side, taking in the lab, the machines, the desks, the computers.

Her eyes fell on Sans.

She paused. She stared.

Sans stared back.

Then Gaster put his hand on a lever on the machine and pulled down.

And she screamed.

He thought he had heard the loudest screams she could produce the day before. He had thought that was as bad as it could get, even though he knew, he _should_ have known, that that was only the beginning. Gaster never did the worst things up front. But he had thought … he hadn’t started with the worst things for _them,_ but maybe for a human …

Maybe he was stupid enough to believe that the human would be much different than them.

But she _was._

Because while Sans was sure there had been some regret, some hesitation, when Gaster first did his experiments on them, there was none now.

The little girl thrashed against the straps, her voice cracking, tears streaming down her cheeks, and didn’t even flinch.

And Sans just stood there. Staring. Watching. Listening. It was like having his soul sliced into, he had never thought a sound could hurt this bad, why did this hurt, it _shouldn’t_ hurt, it wasn’t him, it wasn’t even his brother, it was just some human and her being here going through this meant Papyrus didn’t have to. But Papyrus wouldn’t have wanted this, Papyrus would have _hated_ this, he would have gladly gone through this a thousand times if it meant she would be spared.

His eyes snapped up to Gaster, standing next to the machine, staring at the control board. He was turned half away, but Sans could still make out his face.

Blank.

But not the same kind of blank expression he had worn when he was trying to pretend something Sans or Papyrus said or did hadn’t affected him.

It was just … blank.

Like he didn’t care.

Like he didn’t care at _all._

Like he couldn’t even hear her.

For what felt like an hour, but must have only been one or two minutes, the machine hummed, and the human screamed. Then Gaster nodded to himself and pressed a button in front of him.

The hum of the machine faded, and a few seconds later, her screams began to die down as well—though whether that was because of reduced pain or exhaustion, Sans couldn’t tell. He watched as Gaster flicked off the last few switches and the sound died faded away.

Silence had never felt so empty.

“That’s all we can safely extract for now. Taking more at one time might not give its body time to replenish itself,” Gaster muttered, more to himself than to Sans, marking something down on his clipboard. He opened a small panel next to the controls and pulled out what looked to be a small glass vial, half-full with red liquid, dark and thick, like over-cooked tomato soup. “We may be able to get some more later today, but for now, I have several other tests to run.”

He set the clipboard down on his desk, picked up another empty vial, and transferred every last drop of the liquid before returning the first vial to the machine. Then he began looking around the room, nodding or shaking his head at each machine he examined. Sans watched him, taking in the comfort, the _familiarity_ of his movements. He didn’t even look like he had to think. Think about exactly what he was going to do, sure, but … it was like he hadn’t heard the screams. Hadn’t watched a human kid thrashing about on a table in pain Sans didn’t even want to imagine.

Couldn’t see her lying there now, tears streaming down her cheeks, even as her body remained limp, consciousness abandoned the second the pain had disappeared.

A crease formed in the center of his browbone as his eyes locked on the man across the room.

“you’ve done this before.”

Gaster froze, then turned to look at him, half his browbone raised.

“Pardon me?”

“you’ve done this before. on a human,” Sans repeated. He crossed his arms over his chest and stared at Gaster with hard eyes. “when we first started the experiments. with me. all those baseline readings you had for humans … how they healed, if you hurt them, if you give them electric shocks … you did all this before.”

Gaster held his gaze in silence, before something flashed across his face and he turned away before Sans had a chance to read it.

“I’ve never done this particular set of experiments.”

“but you did all those other ones,” Sans replied without missing a beat. It was so obvious. How could he—he had seen the files, he had _read_ the files, he _knew_ what Gaster had done, but he hadn’t … he hadn’t _thought_ about it, it had just been words and numbers, he hadn’t thought of that stuff actually being _done,_ not on something _alive,_ not on something that could _feel._

He had felt all that stuff. He had felt how much it had hurt.

And he had consented to it. He was an adult who willingly underwent experimentation.

This human never consented. _That_ human never consented.

… had the last one been this small, too?

Gaster pressed his mouth into a thin line, but Sans couldn’t make out anything else from the angle at which he stood.

“I performed a number of tests on one of the humans who fell, before its soul was collected, in order to better understand the physiology and soul properties of a living human,” he said after a very long pause, his words slow and careful, as if he had handpicked each one from a pile of sludge.

Sans looked at the human out of the corner of his eye, but couldn’t bring himself to turn his head.

“before you killed them.”

“I didn’t kill it,” Gaster snapped out, too fast to be a lie, too fast to hide the emotion behind the words.

He was turned away, but Sans still stared at him, took in every detail of his posture. He could barely recognize this man as his dad anymore, but some things hadn’t changed. The way his shoulders formed a sharp line when he was nervous or upset, the tone of his voice when he didn’t want to talk about something, the way he brought his hands close to his torso in some sort of subconscious defense.

Maybe he hadn’t actually changed that much. Maybe this man had been here all along, and Sans had just never had the chance to meet him.

“have you ever killed anyone?”

Gaster jerked around to face him, so suddenly and awkwardly that for a second, Sans couldn’t draw a line between the man who would torture his sons and the man who carted them around in a baby carrier while he worked in the lab because he couldn’t bear to set them down.

“What sort of question is that?”

“have you?” Sans asked again, his arms tighter against his chest.

Gaster looked at him, just looked at him, for a very long moment. Sans tried to read the tilt of his browbone, the lights in his eyes, the tiny movements of the rest of his body, but for once, he came out blank. Or maybe it was just too difficult to admit that that expression looked exactly like his dad’s.

“You’ve known me your entire life, Sans,” Gaster said at last, so quietly, so slowly, so _familiar_ , that Sans felt sick. “Do I seem like a murderer?”

Sans’s smile tightened, and by sheer force of will, he kept his gaze ahead. “i don’t know what you seem like anymore.”

Gaster’s mouth pressed even thinner than before, so Sans could barely make it out even with the small distance between them.

“I’ve never killed anyone.”

It was simple, matter of fact, and as hard as Sans tried, he couldn’t find a hint of lie anywhere in his tone. Then again, it wasn’t like he had had a lot of time to learn how to recognize one.

Before he could say anything else, Gaster turned away, back toward the human on the table.

“It’s waking up,” he said, and immediately, Sans’s eyes snapped to follow his gaze, finally noticing the faint shifting of the tiny body where it still lay strapped in. Gaster started forward. “Come on, if it’s recovered enough to regain consciousness, then we should be able to safely begin another experiment. Perhaps another one of the baseline tests before we attempt another extraction.”

“she.”

Gaster paused, then glanced over his shoulder without fully turning around. “What?”

“papyrus said it's a she,” Sans repeated, very quietly, and with a quiet, sad tone to his voice that he couldn’t hide.

Gaster didn’t reply. He looked away again, and this time, Sans didn’t even try to read his body language. It wasn’t worth it. It didn’t matter. Knowing wouldn’t change a damn thing.

“We need to begin,” Gaster said, and without so much as a pause, he started off toward another machine to get it started up.

Sans didn’t want to stay. He didn’t want to see this again. He didn’t want to see any of this, he didn’t want to be here, he didn’t want this to be _happening._ But it was. And if he wasn’t here, if he didn’t help …

Gaster wouldn’t stop. He would find a way to do this, even if Sans refused. And if Sans wasn’t here, monitoring the experiments, if he didn’t know what was going on … he was only putting himself at a disadvantage. He was only making it more likely that Gaster would find a reason to bring Papyrus in yet again.

If he was here, maybe he could do something. Anything. He didn’t know what. He didn’t know how. But at least it gave him a chance.

No matter how much it hurt to do so.

Gaster rolled one of the machines over to the table, positioning what looked like the arm of a laser gun close to her chest. As he scurried around the lab, muttering to himself and jotting down notes, hooking up what looked to be a wired remote control to the machine, Sans found himself approaching the table himself. He didn’t know why. It wouldn’t help anything to look at her. It wouldn’t make any of this stop. It wouldn’t help _her_. All it would do was make him remember who they were hurting.

Maybe that was why he couldn’t stop.

He stood a couple of feet away from her, even though he knew she couldn’t move more than an inch in those straps. She didn’t seem up to fighting anyway. Her body was limp, her already-light skin even paler, her fingers trembling and twitching against the table below her.

Her eyes were open.

Only halfway, and they were glassy, unfocused, as if she was still working her way back into consciousness. But she was definitely awake, and definitely looking at him, her head tilted just enough to meet his eyes and her face twisted into a mixture of emotions he didn’t want to know how to read.

He considered looking around for some form of sedative. He wasn’t sure if there were any here—wasn’t sure if Gaster had been using them with Papyrus most of the time—and even if they were, they were for skeletons, not humans. But still …

“Sans. Hurry up, we’re starting.”

He looked at the human. The human looked back. She had heard Gaster, and she was conscious enough, if barely, to know what he meant.

He dropped his gaze to the floor. He was close enough not to have to look at her moving, but he could still hear her shaky breaths, still make out the whimpers that filled the near-silence in the room. Somehow, he knew he would have heard them no matter what.

“Please … no more, please … it hurts … please stop …”

It was barely louder than a whisper, weak and pained and scared, but it might as well have been a scream for how hard it made him jolt. He glanced up at Gaster—no reaction, how could he not _hear_ her—then, against his better judgment, back at the human. She was looking at him. Staring at him. _Pleading_ with him, without even needing to say a word.

“I … please, I wanna go home … I just wanna go home … please …”

There were tears growing in the corners of her eyes, but she didn’t cry. Sans wondered if she had any tears left. Could humans run out of tears? She had cried a lot yesterday, she might have cried all night for all he knew, maybe she had somehow run out, but she didn’t need tears to look at him and make him feel like he was looking at a child, _any_ other child, she was just a kid, monster kids, human kids, _who the fuck cared which it was they were all just kids._

A kid. Strapped down to a table.

The same table Papyrus had been strapped to.

Being tortured.

Just like Papyrus was.

Except she hadn’t agreed to it.

She opened her mouth again, but then the machine began to hum, and she clamped it shut, squeezing her eyes so tight they looked like little more than wrinkles. She thrashed against the straps, more quickly now, whimpers slipping past her lips. Sans forced himself to return around, forced himself to ignore her cries, forced himself to walk across the room and turn around and look at her again.

Not a second later, the laser shot out, and she screamed.

Sans didn’t even know what it was doing. He hadn’t asked. He didn’t want to know. He didn’t want to see this, he didn’t want to hear it, he didn’t want to _be here, he wanted to go home, he wanted to hug his brother and pretend that everything was okay and none of this had ever happened—_

She screamed louder, and Sans stared at the floor.

Was that how Papyrus had sounded? Had Gaster ever used this machine on him? Sans didn’t remember it, but Gaster could turn out new machines in days if he wanted to. Or maybe he had dug it out from some old experiment with that other human, years ago.

Either way, from a glance in his direction, it looked to be in good condition now. And Sans doubted Gaster had had time to fix it up since yesterday.

Had Papyrus screamed like this, every evening, every weekend, when the lab was too empty for anyone to hear?

How many things had his brother endured, how many things would Sans never know about because his brother would never tell him?

Because he had failed him. He had failed him before, and he had failed him now.

He let his brother get hurt.

Then he made him give up the one person he had wanted so badly to protect.

He was a coward. He was a fucking coward.

But he couldn’t digest the thought of taking her out of here, and risking the chance of Papyrus taking her place.

So he just stood there for the rest of the day, completing small tasks when he was asked and listening to the alternating crying and silence, the experiments melding into each other until he could hardly tell when one ended and the other began.

By the time he left the lab, they had two full vials of S.E., and the human’s voice had faded to a croak.

He swore, even when she couldn’t make any noise, he could still hear her scream.


	34. Chapter 28

**Notes for the Chapter:**

> And so it continues ...

By the time he got home on Sunday, Sans felt like he could lay down and die then and there.

He couldn’t, of course, as tempting as the thought was. A tiny part of him had still hoped that he could come home and find Papyrus waiting for him, ready to give him a hug and comfort him and tell him everything was okay and he loved him and they were going to make everything right again and let’s eat some delicious food and take a nap, Sans.

Papyrus didn’t come to him when he got home, though. Sans walked into the living room to find it empty, and even though he made plenty of noise downstairs, even though he was just about certain Papyrus was in his room, his brother never showed his face.

Sans couldn’t hold it against him.

He tried to go to sleep a while later, but he found it even more difficult than he had the night before. He slept a little, probably. But it was light sleep, troubled sleep, the sort of sleep where you closed your eyes and things faded but you never dreamed and you swore you were still thinking and when you opened your eyes you weren’t sure whether two minutes or two hours had passed.

He was tired. He was _exhausted._ He didn’t think he had been this worn out in his entire life, even after the first experiments where he had been the subject. It was a different kind of tiredness now. That had been physical tiredness. This was … it was like his _soul_ was tired. Like all his magic, all his energy, had been sucked out of him, and now he was just an empty shell.

Yet even without sleeping, even though it was torture lying there sleepless in his bed, it still took all his willpower to drag himself out of bed, down the stairs, and back to the lab the next morning.

It wasn’t as bad on Monday, at first. Gaster was more careful when the other scientists returned to the lab, and he wasn’t about to risk the human making noises to get someone’s attention—not that she had any reason to believe that the other scientists would care. He even offered to let Sans take the day off. Sans went back to his lab, briefly, but after half an hour of staring at the machine without making a single move to tinker with it or even take notes, he returned to the main lab and sat by the wall, eyes locked on the floor, trying to ignore the unconscious human in the middle of the room.

He knew it wasn’t going to end when the clock struck five. He knew that. And he would have thought that by now, he would be smart enough not to hope for the impossible.

He hoped anyway.

The hopeful voice in his head sounded like Papyrus.

Ten minutes after five, Gaster began putting some things together, gathering supplies, moving machines, making notes. And thirty minutes after five, after the entire building had cleared out, he got to work.

Sans had known it was going to happen.

But that didn’t make it any easier.

It went on until at least nine, experiment after experiment, taking notes and turning machines on and off and following instructions he paid little attention to. Hearing the human cry out for him, until she finally realized that that he wasn’t going to respond, and just cried, sometimes wordless sobs, sometimes curses more vulgar than he would have expected of someone so apparently young, sometimes screams and pleading for someone who wasn’t there.

No matter what she said or didn’t say, nothing changed.

And when he went back to work the next day, it all started over again.

He stopped counting the days that passed. It wasn’t that many—it couldn’t have been more than four, or maybe five, and he knew it had been more than two. They blended together, and without really sleeping it didn’t feel like there was a space between them. It was just one long day, stretching on and on, the same thing when he came home, the same thing when he got to the lab, the same thing when he left. Sometimes he managed to get to his lab in Waterfall and get some work done. Sometimes he didn’t. Sometimes he couldn’t remember why it mattered.

He didn’t pay attention to the experiments Gaster performed. They were almost always the same nowadays. S.E. extraction, several times a day, with recovery time in between and occasionally some other tests to fill in the blanks he had left from his initial run of experiments.

Honestly, he wasn’t even sure if the human noticed what was being done to her. She certainly didn’t understand it, probably not even as much as Papyrus had. All she knew was how much it hurt.

How much it made her scream.

Sans swore that even when she stopped screaming, he could still hear it echoing in his head.

She cried out names sometimes. Names he didn’t recognize—maybe friends, maybe family members, he swore he caught something starting with an L that was cut off by another scream—and names he didn’t _need_ to recognize. Because as much as he had heard about humans being vicious and heartless and violent and merciless, apparently even they still had moms and dads, and apparently they still cried out for them when they were afraid.

Once, she cried out for someone called Toriel.

Sans felt like he should recognize the name. But he couldn’t place it, and honestly, he didn’t want to try.

She screamed and cried for someone to help her. No one did. She screamed for Gaster to stop. He didn’t. Eventually her voice grew hoarse, and broke every time a sound left her mouth. Still she cried, harder and harder. She screamed that this wasn’t fair, that it didn’t make sense, that she hadn’t _done_ anything, she didn’t want to hurt anyone, all she wanted to do was go home.

No one listened.

Sans wasn’t even sure if Gaster could hear her.

He was put in charge of taking care of her. Not officially—maybe Gaster would have taken up the job if Sans hadn’t. But he did. He didn’t know why. Maybe it was his way of dealing with the guilt that threatened to drown him at any second. Or maybe it was just reflex. He didn’t know. But he did it anyway.

There wasn’t much to do. He knew enough about what humans needed to survive from the—very short—book he had read in college. They needed food, just like monsters did, and they were dependent on water, as apparently their bodies were mostly composed of it. From what he understood, usually, they would need to use a bathroom—which apparently didn’t need to have a bath in it, that didn’t make any sense at all—but human food was processed differently than monster food, and though there was nothing in the books about it, he suspected that the bathroom thing wouldn’t be required.

Gaster didn’t comment about him feeding her, but he didn’t stop him either. After all, the human needed to be alive for him to continue the experiments, and from what Sans understood, humans would die very quickly without some sort of nourishment.

She didn’t accept it the first time he tried to feed her. She just begged him to let her go, begged him to stop all of this. Then, when he didn’t reply, she snubbed him, closing her mouth so that even if he had tried to force the food in, he wouldn’t have been able to do it.

After the first day, though, she took the food, without looking at him, without saying a word. She just laid there and chewed and swallowed, occasionally choking a little—Sans got the impression humans didn’t usually eat lying down. Sometimes she took it easily, and sometimes he had to push it past her lips, or even open her mouth by hand to put it in. He thought she might try to bite him when he put his fingers near her teeth. She never did. He tried not to wonder why.

The number of meals that were virtually force-fed increased by the day, until breakfast today, which he almost had to fight her to get it down. She didn’t have enough energy to put up a real struggle, but it was far more difficult to force someone to eat when they didn’t want to than he would have imagined. Especially for a human. While monster food might have disintegrated the second she swallowed it, humans apparently didn’t fare well with large portions of food going down their throats without chewing first. And he couldn’t exactly force her to chew.

But she ate, even if it wasn’t as much as she really should have. And as soon as he set the plate aside, the day began as usual.

At least until early that afternoon.

Gaster had left the lab a little while ago. Sans didn’t ask where he was going. He left sometimes—albeit rarely—if he realized he was missing some part for an experiment or the machine needed to be oiled and he had run out of oil. Either way, Sans knew it wouldn’t be the end of the experiments for the day. It was far too early for that.

The lab was quiet on his own. Or … not quite on his own. He sat in one of the rolling chairs and stared at the clock for a good ten minutes, watching the hands tick by. He could hear the human breathing across the room. He wondered if all humans breathed that loud, or if it meant something was wrong with her.

He didn’t have a set time for feeding her, so after those ten minutes had passed, he pushed himself out of his chair and slipped out of the lab, down the hall toward the vending machine. He could hear the faint chattering of voices when he passed Dr. Frewth’s lab, the laughter as Dr. Frewth finished a joke and the returning snickers of the intern. And for a second, Sans swore everything was okay.

Then he moved away from the lab, and the sound disappeared, and the world was crumbling around him yet again.

He bought a few candy bars from the vending machine and carried them back to the lab, picking up his pace when he passed Dr. Frewth’s door, if only to avoid hearing the voices again. Normally he would have brought something halfway-nutritious from home, but candy bars at least had energy, and maybe she would be more inclined to eat if the food tasted better.

She hadn’t moved when he got back. Of course, with the straps holding her in place, she couldn’t actually go anywhere, but he swore she hadn’t even shifted. Her bright orange hair still fell around her head in exactly the same pattern, looking empty without the hat Gaster had taken off and put on one of the tables to “get out of the way.” Her skin looked just as dull, paler than before, dark circles around her eyes. Lips dry and cracked. Body limp.

Her eyes were open. He couldn’t remember if they had been that way before.

He unwrapped the first candy bar and approached her, slowly, like he might approach a frightened animal, even though there was no way for her to attack him. He tried to smile, even though she must have known it was fake, if it even looked halfway convincing in the first place. She didn’t move. She barely even seemed to breathe.

Sans touched the candy bar to her lips. Nothing. He pressed again, a little harder, waiting for her to bite a piece off, even scrape a little of the chocolate coating off with her teeth. But she didn’t. Just like this morning, she didn’t even seem to notice the food was there. He tried again, and again, and again after that. No matter how hard he pressed the food toward her, she refused, without saying a word.

“hey,” he said, his voice croaking before he cleared his throat. She didn’t respond. He came close to shaking her, but pulled his hand back at the last second. “hey, kid, c’mon. you gotta eat.”

She didn’t move. Not a blink, not a twitch. She was alive, she was breathing, he knew she wasn’t dead yet, but she wouldn’t even _move._

He gritted his teeth. “kid, if you don’t eat something, you’re gonna die. you don’t wanna die, do you?”

Nothing. She should be moving, she should be upset, she should be yelling at him, even just _glaring_ at him, communicating to him exactly how much of a piece of scum he was.

He let out a long, trembling breath, his fingers so tight around the candy bar in his hand he almost crushed it.

“please, kid. c’mon …”

The words didn’t sound like his words. He started talking and words came out and he didn’t know where they came from. It was what Gaster would want him to say. Well, maybe not—Gaster had already talked about tube-feeding the kid if she didn’t accept food the normal way.

Maybe it was what Papyrus would have said. Papyrus would have wanted the kid to eat. Papyrus would have wanted the kid to live, of her own free will.

As soon as the thought crossed Sans’s mind, he snorted.

No. Papyrus wouldn’t be letting this happen at all.

He tried a few more times, and finally resorted to breaking off a tiny piece and pushing it past her lips, then another, and another. Her cheeks puffed up, but though she chewed, he was pretty sure she didn’t swallow more than a little. After all of the first candy bar was gone, he gave up, shoving the rest into his bag. He would try again tonight. Maybe she would be hungry enough to eat then.

It was a small hope, but it was all he had.

Then again, maybe he was just being selfish, trying so hard to keep her going, when she had so obviously given up.

She was alive. But it was like saying someone who had already fallen down was alive. They hadn’t turned to dust yet, but they weren’t _there._ They couldn’t speak, they couldn’t move, as far as anyone knew, they couldn’t even hear those around them. They were just … there.

Sans had heard some monsters say that once you had fallen down, death was a mercy.

He still hadn’t decided whether or not he believed it.

Gaster didn’t seem to have noticed. The only thing he noticed was that the production of S.E. had slowed down. She had been fed physically, sure, but even though Sans knew humans weren’t as connected to their souls as monsters were, he would have to be an idiot not to notice her emotional state connected to the health of her soul.

And even if her body survived, her soul was dying.

He had never heard of a human falling down before, but he was beginning to wonder if this was what it looked like.

He wondered what she was thinking, if she was thinking anything. He wondered if she could even feel the pain she was going through during the experiments. He wondered if she could hear him when he talked to her.

He wondered if she felt like he did.

Empty. Alone.

He wondered if it would have been easier to be in her place. To feel the pain rather than listen to someone else screaming. She probably would have done anything to be in his place, but all he wanted was to be in hers.

He didn’t want to feel any of this. He would rather go through those initial experiments a thousand times over than be here right now. Maybe if he hadn’t quit, if he had kept up with the experiments, it wouldn’t be this bad. Maybe Papyrus would have been able to hide the human, and he wouldn’t have been in danger in the first place, since Gaster wouldn’t have needed anyone to take Sans’s place.

Maybe Papyrus would still be talking to him. Looking at him. Hugging him when he came home.

Maybe he wouldn’t hate him quite as much as he did now.

But Sans was too weak for that. He was too weak to keep going with the experiments, too weak to stop Gaster when he started experimenting on Papyrus, too weak to keep the human from him, too weak to risk anything happening to his brother now. Too weak to protest. Too weak to do anything but follow orders.

Maybe that was why he was here right now. Maybe he deserved it. Maybe, if he had been stronger, strong enough to stay with the experiments … strong enough to refuse them in the first place, to shut his dad down before he could dive in headfirst … strong enough to turn his dad in and lose the person he had admired most since the day he was born …

The doors to the lab opened, and Sans’s head snapped up, his eyes wide and blinking, searching for Gaster.

But Gaster didn’t come in.

He stood just in the hallway, but there was someone else in front of him, stepping through the doors.

Tall and thin, wearing a deep red turtleneck and long pants, his hands held close to his torso, his eyes locked on the floor.

Sans pushed himself out of his seat, breath caught in his throat.

“pap?”

Papyrus looked at him. Just for a second, but it was more than he had gotten in _days_ and Sans soaked it in before it was yanked away as Papyrus’s gaze fell back to the floor.

He remained in the doorway as Gaster walked around him and further in, striding toward one of the tables to grab his clipboard.

Like he did before an experiment.

“what’s he doing here?” Sans asked, even though he didn’t need to, even as the pieces clicked into place in the back of his head.

“He’s here for initial testing, of course,” Gaster replied, as if it should have been obvious. Sans’s sockets grew. Gaster looked over his shoulder. His eyes scanned over Sans’s expression, and his face softened in something like pity. “Sans, Papyrus has already absorbed a good deal of S.E. If he absorbs enough, he could be the equivalent of a seventh soul. We wouldn’t even need to synthesize another. This is the most logical course of action, the quickest way to get through this. You must have realized that by now.”

Sans couldn’t speak. He couldn’t think. Gaster looked at him for a few seconds longer, and god, he looked sad for him, he looked almost _guilty,_ but it was the same kind of guilty look he had worn before he reset Sans’s arm when he tripped and broke it when he was eleven. Pained, so genuinely pained, but with the underlying certainty that _it was the best thing for him, it was the right thing to do, it would hurt for a second but it would be so much better in the long run_ —

Gaster turned back to his brother, motioning toward one of the empty chairs nearby.

“Now, Papyrus, go sit down, I’ll be there in—”

“use me.”

Gaster stopped.

Moving in perfect synchrony, he and Papyrus turned to face Sans.

“I’m sorry?” Gaster asked, a breathy confusion to his voice that Sans had almost forgotten.

Sans curled his hands into fists so hard they trembled, his teeth gritted, his eyesockets completely black.

“Use me,” he repeated, more firmly this time, lifting his head to hold himself as tall as he could. “If you’re gonna give the S.E. to someone, give it to me.”

Papyrus stiffened, breath catching in his throat. He opened his mouth as if to say something, but no words came out. Gaster didn’t notice. He just stared at Sans, and Sans swore there was the briefest flash of something like pain in his eyes—why wouldn’t it go away, it would make all of this so much easier if he would just stop looking at them _like he actually gave a damn_ —before it vanished again. He sighed.

“Sans, we’ve already gone over this. Papyrus—”

“He can withstand _damage_ easier than I can, sure, but what does that have to do with S.E.? I’m just as valid a test subject, and we have enough S.E. to start from scratch with me. Besides, who will be more useful once we get to the surface and have to deal with the humans there? Papyrus won’t hurt them, he _proved_ that with this one, you don’t know if he’d ever break the barrier,” Sans replied. It hurt. God, it hurt like hell, it was like agreeing every time people said he was better suited for something for his brother, better at science, better at math, better at school, better at _all these things that didn’t matter, they didn’t make him better than his brother, he could never be better than his brother, he wasn’t_ half _as good as Papyrus._ Sans closed his eyes and took a deep breath before lifting his gaze again. “I won’t fight. I’ll do it willingly. As much as you want. _Whatever_ you want. Just … let him go home.”

Silence.

Papyrus stared at him with eyes wider than Sans had ever seen. His mouth opened, but no sound came out, his hands trembling in front of him and his shoulders hunched, he looked so small, so young, so afraid, and all Sans wanted to do was protect him, get him away from this, even if he couldn’t get his brother back, at least he could keep him safe.

“sans …” Papyrus murmured, and it was barely louder than a whisper, but it felt like a scream.

Fear. Horror. Pain.

Papyrus closed his mouth, then opened it again, as if he might try to protest. But Sans shook his head, just enough for him to see, begging, _pleading_ to just let him do this. He had failed as a brother in every other respect, just let him help, just once, let him do _one thing right in this whole goddamn mess._

Gaster’s breath came out in a long, heavy sigh.

“Very well.”

Sans’s head snapped to the side, his eyes wide, and a second later, Papyrus had already jerked his head to stare at them both, his face twisted into something so _pained_ that it made Sans hurt even worse just to look at it.

“What?” Sans asked, browbone furrowed as he tried to figure out whether or not he had just been imagining things.

Gaster didn’t look at him. He faced him, but his eyes had shifted to the side, his mouth pressed into a tight line that should have made Sans feel satisfied—anything that proved he had some _inkling_ of the sick shit he was doing—but now, he couldn’t bring himself to feel anything at all.

“You’re correct,” Gaster went on, more clearly this time. He glanced at Papyrus, then Sans, then sighed again. “Though there are certainly risks associated with these experiments, I don’t think they will carry the same threat as previous procedures. This might have some more beneficial effects, in fact. And with a living human … we can gather all the S.E. we need.”

Sans should have felt relieved. This was what he wanted, wasn’t it? Papyrus would be free. Papyrus would be _safe._

But it was nearly impossible to feel anything good when Papyrus was looking at him with such horror in his eyes.

“If you’re so insistent on doing this yourself, Sans, I won’t argue,” Gaster finished, snapping Sans’s attention back to him. But Gaster’s attention shifted only a second later, meeting Papyrus’s gaze before turning away again. “You can go home, Papyrus. We’ll see you this evening.”

Papyrus didn’t move. He just stared, looking back and forth between Gaster and Sans and the human, still resting unconscious on the table. His eyes lingered on the human, his body leaning forward, as if he might run and grab her. He didn’t. He looked at Gaster one more time, then he looked at Sans, just long enough for Sans to see the horror, grief and betrayal warring on his face.

Then he turned around and walked out of the office, his arms clutched so close to his ribcage they almost disappeared within it.

Gaster made a gesture toward one of the nearby chairs. His eyes remained on the door, falling shut behind Papyrus, even as he crossed the room and sat down where Gaster had indicated. He wasn’t sure whether it was him or Gaster that took off his shirt, and he didn’t care. He felt the wires being hooked up to his body, the hum of the monitor as it read his baseline vitals. But he didn’t look at it.

He didn’t even notice Gaster picking up the needle until he felt the pinch next to his shoulder.

He counted down in his head, almost without realizing it. He felt the needle dig into the bone, felt the plunger go down, felt the liquid seep right into his marrow. He waited, counting each second that ticked by on the clock by the wall.

And just as he reached eleven, the fire hit.

Sans choked on his own breath, the air rushing from his body as he jerked forward, almost hard enough to fall from the chair. His fingers and toes curled in almost tight enough to snap, his sockets squeezed shut, god, oh god why, he had had his soul sliced into, this shouldn’t hurt so bad, and it was spreading, flooding down his arm and through his torso and out into his other limbs, it was in his skull, it was eating him, burning him alive, had he fallen into a lava pit, was this what lava felt like, he was going to die, he would die and this would all be over and Papyrus would be alone but that would be better he wouldn’t have to deal with his stupid useless brother ruining everything he had ever—

He breathed.

The feeling faded so fast he almost fell over, leaving behind the sort of overwhelming ache he might expect after running across the entire underground without stopping. His fingers relaxed, his body wobbled, and he panted, gasping in as much air as he could take in, he didn’t need to breathe, so why the hell did it feel like he was suffocating?

He didn’t notice his entire form trembling until he felt the hands nudging him back, settling him further into the chair so he wasn’t so close to falling out. His eyes squinted open, just enough to see the blurred, tall white form standing in front of him.

He tried to talk. Tried to say his name, he knew that face, he knew those gentle eyes, watching him with panicked concern, he knew those careful hands that had carried him through the worst moments of his life, he wanted to lean forward and rest in his arms, rest in his _dad’s_ arms, just let him hold him and know that everything would be alright.

Then the hands pulled back.

His eyes opened further, and his vision began to clear.

And he stared back into eyes that clashed with concern and blank, curiosity.

And he remembered.

As soon as he could make him out clearly, Gaster turned away, focusing his attention on the monitor next to the chair. He wasn’t reading it. Not really. He just wanted something to look at, so he wouldn’t have to watch Sans’s expression shift as the pieces clicked in his head, one by one, until the picture was complete.

“that’s what you did to Papyrus,” Sans breathed, so quietly he almost couldn’t hear it himself. Gaster stilled, but didn’t turn to face him. Sans took in a few more breaths, sucking it in as if he actually had lungs to fill. “four times.”

Still nothing. If he looked very closely, he could see Gaster tense up. But it was so slight he could barely see it. Maybe he was imagining it. Maybe had been imagining it every time he thought he had seen it before.

“that’s what you were going to do to him again.”

Maybe he had imagined everything. Maybe he had imagined those kind, gentle smiles his dad gave them when they were growing up, the hugs, the encouraging words, the proud shine in his eyes every time he accomplished something. Maybe he had imagined a shiny, smooth plane of glass and had failed to notice the cracks running through it, deeper and deeper until finally it shattered and he wondered how he had ended up with a mess of shards all over the floor.

Sans gritted his teeth, his body trembling yet firm all at once.

“i hate you.”

It sounded wrong. It sounded so wrong he wanted to yank it out of the air and shove it back down his throat. But he still couldn’t move his arms or his legs and it still felt like he was going to die and for a second, just a second, he meant it. For a second, he wanted to give up on the machine and on the man who had once been his dad and take his brother and leave for good.

Gaster closed his eyes and pressed his mouth into a thin line.

“I know.”He paused, letting the silence linger between them like gaseous acid, eating away at them until they were raw and burning but still there. Always there. No matter how bad it got.

Then he turned to the machine, picked up his clipboard, and began jotting down his notes, while Sans sat in his chair and watched and hurt and tried to remember what things had been like before this mess had begun.


	35. Chapter 29

**Notes for the Chapter:**

> Body horror, child torture, blood, and buckets of family angst. Have fun!

Sometimes Sans forgot why he was building the machine.

He would slip off in the evenings, or in the middle of the night, or whenever he could get a minute to himself, go back to his private lab, and just stand there, looking at the machine, trying to remember what the point of it was.

He would trace his thought process back, remember what the machine was supposed to do, and try to imagine what he had been thinking when he first designed it. He wanted to go back in time. He wanted to go back and change something important. Something had gone wrong, and he wanted to go back and fix it.

Then he would think about what had happened to change all of this. When the man who had loved him, cared for him his entire life had lost his gentle touch, when he had focused more on the results of the experiment than how the experiments affected _Sans,_ when he had been so desperate to continue with his research that he had dragged Papyrus into this whole mess. And he would remember all the things he had said, how many times he had said it would be worth it, how many times he had insisted his dad continue, how many times his dad tried to stop and Sans _wouldn’t let him._

And then he would be quite sure that he was building the machine so he could go back and strangle himself.

He would hear Papyrus’s voice in his head sometimes, telling him that none of this was his fault, that he couldn’t have known how far things would go, that he couldn’t blame himself for any of this. But it was always distant, and stilted, and it wasn’t _really_ Papyrus’s voice and all he wanted was to hear his brother’s voice telling him everything was okay but he was never going to get it.

He would have gotten it if he had deserved it.

Even when he finally remembered the point of the machine, he still wanted to go back and punch himself in the face.

Every day, Sans went to the lab, just as he had before. But unlike before, now, as soon as he arrived, he sat down in the chair for Gaster to inject him with another small shot of the S.E. At first, he thought maybe they were smaller shots, or maybe it hurt less as his body adjusted to it. At least until his saw Gaster’s notes on his physical responses—as tense and comfortable as the first time—and wondered whether he had just stopped reacting to the pain.

It was like a dream. A long, unpleasant dream.

It had been a week, apparently. He hadn’t known until yesterday, when he came back from the lab and found himself stopped by one of his neighbors. His mind was too muddled to remember their name, but he knew them. Probably.

They had asked him how work with the human was going.

They had asked him if their soul could be used to break the barrier.

And Sans just stood there, staring at them, for a good minute, before he turned and walked the rest of the way home.

The barrier. That was what this was meant to be for, wasn’t it?

He had forgotten.

He had forgotten all of this was supposed to have a purpose. He had forgotten why they had started in the first place, what excuse Gaster still used for what he was doing. For making the human scream. For making Papyrus spend all day huddled in his room. For sitting Sans down in the same chair every goddamn day and injecting more of the S.E., taking what was leftover and placing it in the same container Sans stole from whenever he got the chance.

Sometimes he wondered if Gaster was even trying to make excuses in his own head anymore, or if he was so absorbed in his own work that he had forgotten that the human was supposed to go to the king immediately.

For the first time, Sans found himself wondering if the king had heard about the human’s presence.

He stopped thinking about it as soon as he started wondering whether the king would have approved.

He didn’t know the king very well, but he didn’t really want to know the answer.

The human didn’t move anymore, except for occasional twitches or groans. If Sans hadn’t been able to see her breathing, he would have thought she was dead. They didn’t teach much about humans in school, but he had learned enough back then to know that human bodies didn’t turn to dust like monsters when they died—they just stayed there and rotted away until they were nothing but the bones that apparently held humans together beneath all that other stuff.

He would probably see that now. A dead human. A dead human that started looking like a skeleton.

Or would he? Gaster would have to let the king know he had a human at some point or another—if he didn’t know already—or at least bring him her soul. Assuming he was _planning_ to give the king the soul, and not just shove it inside Sans once he had enough S.E. to pass for a human. Would he kill the human first, then take her soul, or would he find a way to do it before she died and kill her that way? Or did the king want to see her before she died? Did the king actually kill the humans himself, or were they dead when they went to him?

Sans had never asked. It had never seemed important.

He had never thought he would have to deal with it.

He had never thought he might have to watch one die, or that the idea would actually cause him pain.

Was this caring about her? Or was he just so sick of seeing someone strapped to that damn table that he didn’t care who it was, he just wanted it all to _stop_?

Or did he just hate it because it made Papyrus so sad?

She was in pain. More pain than he was, without a doubt. Probably more pain than he had ever been in, maybe more pain than Papyrus had been in. It was hard to tell. She had screamed easier than Papyrus. She had no reason to hold back her screams like Papyrus had—even if her screams had dulled to whimpers now. And it wasn’t like he could ask her how much pain she was in. He wasn’t even sure she would be capable of answering, if she wanted to in the first place.

It sounded like a shitty thing to do anyway.

It sounded like something Gaster would do, taking down levels of pain as part of his notes.

It wasn’t like he could do anything about it.

And it wasn’t like he had much time to think about her being in pain when he spent most of his time in the lab nowadays either following instructions or sitting in a chair, getting poked with a needle and gritting his teeth against the fire flashing through him.

It was Saturday today. Not that he thought weekends were going to be much different than weekdays from now on—before, Gaster had had a reason to make sure no one heard the screaming. But Gaster hadn’t stopped the worst of the experiments on Monday, when everyone came back to the building.

Because everyone knew.

Because no one cared.

Because they knew there was a human there and apparently hearing a human scream wasn’t bad enough for Gaster to hide it.

He had done this before.

Dr. Japer had been there, back then. Had they been friends? Had she known? Dr. Frewth and Dr. Lemming were new, but Dr. Japer … and Dr. Billington, she …

He tried not to think about it.

It wasn’t going to change anything.

He couldn’t even remember the last time he had seen Dr. Japer anyway.

He got to the lab at the same time as usual. He set his bag down on the table and glanced around at the growing disorganized mess, a few blueprints, test tubes, scattered notes, but paid none of it any mind. He stood off to the side while Gaster extracted more S.E. from the human. Her screams were even quieter than yesterday. He doubted it hurt any less than before. Vaguely, he could remember laying on that same table, and feeling the pain of each experiment dull as his energy drained to almost nothing. After a while, it was like his mind began to drift as the pain started up, distancing itself in a last-ditch defense. Pretending that the body suffering through the agony wasn’t even his.

Was that what she felt?

Would she be able to tell him, if he even wanted to ask?

Once the extraction was complete, Sans sat down in the same chair he had occupied for the past few days. Sometimes Gaster would come immediately. Sometimes he would dawdle up to an hour, wandering around the lab, taking notes, maybe running a brief test or two. It didn’t matter. It wasn’t like Sans had anything else to do here.

There was no use trying to sneak off in the middle of the day. With his luck, as soon as he stepped out of the lab, Gaster would finally notice his presence—or lack thereof—and find a reason to come looking for him, even if he never had before. It wasn’t a risk Sans could take.

Even if sometimes he wondered whether anything he was doing had a point at all.

“Sans?”

It was quiet. Quieter than anything Sans had heard Gaster say in a while. He lifted his head, just enough to meet the sockets in front of him.

They looked like his eyes.

His dad’s eyes.

Soft.

Pained.

Sans’s permanent smile tightened, and his eyes narrowed in a glare.

“what?”

Gaster paused for a moment, as if he might actually speak. Then he closed his eyes and turned back to the table. “Nothing.”

Sans let his head fall again without another word.

He felt the same prick of the needle, the scraping of the sharp point against bones as it found its usual spot. He felt the sting of the liquid forcing its way into his bones. He felt the brief relief, thirty seconds tops, when the needle retreated, and Gaster stepped back.

Then the fire returned.

It still felt like fire, even now, even though he had never really been _burned_ enough to know what real fire felt like. But it was like burning a part of his body that had already scarred—or whatever he imagined a scar would feel like, since bone didn’t scar the same way as skin. It was dulled. It was distant. Maybe his mind had already gotten used to the sharp feeling, and refused to process all of it for fear of overwhelming him. Or maybe all the S.E. already in him was just making it easier to bear.

He waited, like he always did. Waited for the minutes to pass, the burning to end. It always did. It never lasted longer than five minutes, even if it sometimes felt like an hour. He never screamed. Not anymore. His body tightened and his fists clenched and his head swam but he didn’t scream, he didn’t even whimper, he just waited. Waited for it to be over.

But the burning didn’t fade.

It grew. At first just a little, barely noticeable, but it kept going, hotter and hotter until Sans thought he really had fallen in a pit of lava, maybe he had fallen unconscious and Gaster had planned some new crazy experiment and was going to drop him in the Core to see what happened.

Would he do that?

Had he gone that far?

Sans’s eyes shot open, and through his blurred vision, he could still make out the white walls of the lab, the forms of tables and chairs and machines.

And one moving figure, rushing around in front of him, too fast, too crazed, for Sans to make out.

But Sans couldn’t move. He tried. He tried to lift his arms or his legs but every time he did he swore he was going to fall apart, he didn’t know what his legs were anymore, they were sinking into the floor, they _were_ the floor, wasn’t he taller than this a few seconds ago, his arms were falling, falling, falling down, he was falling down, this was what it felt like, he was going to die, this was it, this was death, he didn’t even get to see Papyrus smile again—

Something pinched his arm, right near the joint of his shoulder. It hurt, but he didn’t care. Everything else hurt worse.

It took another minute. Another minute in which he was sure that he was going to keep dissolving, that was what he was doing, dissolving into the floor, he wasn’t even going to turn to dust like a proper monster, he was going to _melt_ —

Then it stopped.

And the bits of him that had slipped away began to reform into solid bone.

Sans breathed. He … he tried to breathe, he was sure he could breathe now, he could move his arms, if he tried he could move his hands, and his fingers, just a little bit. He flexed them, looked down at his fingers to make sure they were still fingers, that there were still five of them on each hand, that was how many there were supposed to be, right?

Five. Five on each hand.

All there.

Sans’s breath shuddered so hard he felt like he might shatter now that he had reformed.

He looked up.

Gaster. That was Gaster, wasn’t it? He was still blurry, but cleared more by the second. Standing in front of him, a few feet away, hadn’t he been closer before? He had stuck a needle in him. He had … when he had been … and he was just standing there now, completely still, turned half-away as his wide, blank eyes locked on the floor.

Sans swallowed against the rush of nausea rising in his throat.

“i was … melting.”

Gaster flinched, so hard Sans could almost hear his bones rattle. Still, he didn’t turn to look at him. “Yes.”

“i … i was _melting,_ ” Sans repeated, finally letting the words sink into his head, his breath coming faster as his soul twisted in residual panic.

“Yes, I noticed,” Gaster all but snapped, and though there was still some of that cold indifference there, something like fear shone through.

Sans panted, trying to catch his breath, he didn’t need to breathe, he knew he didn’t need to breathe, but he still felt like he was suffocating. Was this what a human felt like if they couldn’t breathe?

“what the _hell,_ why was i …?”

Gaster’s mouth set in a tight line. He turned a little further away, so Sans could only make out a tiny part of his face.

“Some … unexpected side effects were expected with this, though …” He trailed off, his shoulders tenser than before, like he was debating with himself. Then his shoulders went limp, and he let out a breath. “I stopped it. You’ll be fine. We won’t make that mistake again.”

“what did you do?” Sans bit out, forcing back the panic that still threatened to overwhelm him.

At last, Gaster turned just enough to look at him, his browbone furrowed and his mouth tilted in a frown. “What?”

“how did you stop it?” Sans asked. He stood up a bit straighter, even though his limbs still shook and he had to fight the spinning of his head.

Gaster paused, watching him, taking him in. Sans could almost imagine him taking notes in his head—at this point, he wouldn’t put it past him. Then he looked away again, but didn’t turn, so Sans could still see the tiny shifts in his expression, the tightness of his features, the pain, the _fear,_ that had yet to fade from his eyes.

“Monster bodies appear to be … unable to handle the substances found in human souls. Humans are primarily physical, monsters primarily magical. And the S.E. does not appear to react well to magical material in such high doses, even considering that you were exposed to it from your creation.”

He was avoiding the question. He was good at that, even better recently. Once, Sans might have let it go. But this wasn’t then anymore. Sometimes he could barely remember what “then” had even been like.

“what did you do?”

For nearly a minute, Gaster said nothing. He didn’t move. He didn’t look at Sans. He just stood there, staring at the floor, and Sans stared at him, unrelenting, waiting for the answer he was going to get, one way or another.

When Gaster sighed again, his breath shook so hard it made Sans’s soul twist.

“I injected physical matter to counteract the process. To … give the S.E. in your body something else to latch onto, to keep you together.”

Sans blinked. Then he blinked again. And again after that.

“you gave me … physical matter?”

Gaster glanced at him out of the corner of his eye. “Blood.”

The clock on the wall ticked. Sans’s soul pulsed. His eyes drifted across the room, toward the human lying limp, unconscious, on the table.

And the tiny bandage on the inside of her arm that definitely had not been there before.

“you gave me her blood,” he repeated, his voice as blank as the rest of him felt.

“Just a vial,” Gaster went on, without looking at him at all. His voice had changed again. The concern was gone, the gentleness, the panic Sans swore he had heard in his voice but maybe that was just a hallucination from the pain and the _goddamn melting,_ who knew what was real anymore, except this, _this_ was real, sitting here and watching his dad refuse to meet his eyes when he had almost _died_. “Let me know if there are any lingering symptoms, I’ll inject another.”

Before he could stop himself, Sans felt his eyes drifting down to the spot near his shoulder where the needle always went. He swore he could still feel it now, piercing between two bones, but it wasn’t the same stuff, it felt the same, but it had been … it had been a _part_ of her, not just her soul, her _body,_ blood was important to humans, blood was _life_ to humans, like magic was to monsters, and it was …

His hand trembled, and let his arm fall back down to his side as his eyes rose to Gaster again. Gaster paid him no mind, and after a few seconds of silence, he picked up his clipboard from a nearby table and began peering down at it, as if there were something there more important than what was right in front of him.

“The high level of S.E. might be causing some sort of buildup in your system,” he murmured after a minute of silence.

Sans raised half his browbone, his body still trembling from the reminder that he had been _melting_ a few seconds ago.

“oh, you think?”

If Gaster heard his sarcasm, he didn’t respond. He tapped his pen on his clipboard a few times, then looked up again. “Try your blasters.”

“what?”

“The blasters,” Gaster repeated with a touch of impatience, as if he had expected Sans to automatically follow his logic. “That should release some of the excess energy in your body. It seems that they flourish under high doses, so I suspect using them may stop the S.E. from affecting you so strongly.”

“oh, so maybe i _won't_ turn into a puddle?” Sans asked.

This time Gaster’s eyelights narrowed, just a bit, in something in between irritation and exasperation. It was small, barely noticeable—probably invisible to someone who didn’t know him as well as Sans—but it felt like the greatest success Sans had felt in months.

“Sans, please. This may help you.”

Sans lowered his browbone and gritted his teeth. “since when have you given a damn about helping me?”

Gaster flinched. It was brief, so brief Sans wasn’t even sure if it lasted a fraction of a second. But it was there. And a moment later, Gaster looked away, his mouth pressed into a thin line.

“Everything I do is for you.”

Sans laughed. It was breathy, it was humorless, and it _hurt_ coming out, but the way Gaster’s hands twitched at his side was more than worth it.

“is that what you tell yourself when i’m writhing in pain?” Sans asked, so quiet he could barely hear his own voice, though he had no doubt Gaster could hear him perfectly. He pointed a finger across the room. “is that what you told yourself when papyrus screamed for you to stop? when that _kid_ screams for you to—”

“Enough,” Gaster snapped, sharper than Sans had ever heard him speak. Sans froze, staring, waiting. Gaster sighed and put a hand to his face, rubbing the bone above his nasal package without looking back up. “Just try your blasters.”

Sans looked at him for a few seconds longer. As expected, Gaster ignored him, and the brief spurt of defiance did nothing to soothe the ache in Sans’s chest.

Finally, he bit back a huff and pushed himself out of the chair on wobbly legs. He faced the empty wall across the room, closed his eyes, and summoned the attack from within his soul.

The blasters were … strange. Strange just by virtue of being _weird,_ but also strange because of how fast Sans had gotten used to them. Just a few days ago, he had never used them before in his life, never even seen _Papyrus_ use them, but then he had had his first dose of S.E., and Gaster had gotten curious whether it had the same effect on him as it had Papyrus.

And it did.

And now, rather than just bones, he had a floating skull attack that shot out beams of energy stronger than any bone attack Sans had ever seen.

Or, at least, stronger than any of _his_ bone attacks.

He hated it. And yet … he had never felt so powerful. He had never had any _interest_ in being powerful when he was younger. What good was being powerful when all you wanted to do was spend time in the lab doing research? But now …

Being powerful meant being able to defend himself. To defend those around him. It meant being powerful enough to fight back, if he needed to.

Even if he didn’t have the energy to do much with any sort of attack, let alone a powerful one.

It was petty, maybe. But at this point, when everything good in his life had already been ripped out from under him, he was willing to take anything positive he could get.

He didn’t even need to close his eyes and focus like he had on the first try. He looked at the wall, took a second to aim—and another second to resist the urge to blast something important—and fired.

Light filled the room, blinding, overwhelming, before it faded again a few seconds later.

Sans’s arm trembled, but he dropped it back to his side before Gaster could notice. It didn’t matter. Gaster’s attention was locked on the wall anyway, examining the tiny, almost unnoticeable marks from a distance before stepping a little closer. He hummed to himself, then marked something down on his clipboard.

“I’m impressed,” he said. “You’ve taken to these far quicker than Papyrus did.”

For a second, a split goddamn second, Sans felt his chest swell with something like pride.

Then that pride disappeared, and Gaster’s words repeated themselves in Sans’s head. He wanted to die.

Gaster didn’t so much as glance at Sans as he turned his attention from the clipboard to the wall, frowning and tilting his head as he examined the damage again.

“As for your attack and defense, could you put a bit more effort into it? That barely made a scratch, and I don’t think such a low level output is going to help the side effects.”

The fire had long disappeared from his bones, but now, Sans swore he could still feel it again. Bubbling inside of him, burning, stinging, eating away at his insides until all he could do was stand there clenching his teeth and his fists as Gaster stared at the wall as if it was the only thing in that mattered in the whole fucking world.

“i can’t.”

Gaster paused, turning his head to meet Sans’s eyes at last. “I’m sorry?”

“i _can’t_ ,” Sans repeated, and he couldn’t feel the faint satisfaction of finally being acknowledged over the frustration building within him. “that’s the most i can do.”

Gaster looked at him for a moment, his face blank, before he huffed a heavy breath.

“Sans, that’s ridiculous. I’ve been keeping track of your stats since you were a toddler, and I know you can do better than that.”

“yeah, i could, _when i was a toddler_ ,” Sans bit out.

“What are you talking about?” Gaster asked. Before Sans could reply, he felt the faint, familiar sensation of being checked, the feeling that had once been comforting, had once meant that his dad was ensuring he wasn’t hurt, checking that he had been properly healed, the feeling that now made a shiver run through his bones. Gaster’s browbone shot up as the feeling disappeared. “What in the world happened to your HP?”

Sans stared. For at least half a minute, he just stared. Gaster used that half-minute to check him over again, and again, and a third time after that. Finally, the realization clicked.

“you didn’t know?”

“Why didn’t you say something about this?” Gaster asked, as if he hadn’t heard him. Sans couldn’t tell whether he sounded more concerned or irritated. “If the S.E. is causing further side effects—”

“this isn’t the s.e., you idiot.”

Gaster froze, his mouth still open, his eyes wide as he stared at Sans with a blank expression. He paused. His mouth closed. He blinked.

“Excuse me?”

“you think this is the _fucking_ s.e.?” Sans all but hissed, his soul burning in his chest, he could feel the S.E. now, bubbling in his bones, it wasn’t gone, it was never gone, it stayed there, and he could _feel_ it, not just with an attack, it was always there, it had always _been_ there.

Gaster had _put_ it there.

“do you not _see_ what you’re doing to me? to that human? _to papyrus?_ do you not _see_ that you’ve ruined _everything_ for us? we were fine before, but now? did you _really_ think this wasn’t gonna have any consequences? did you _really_ think we’d get out of this like some happy dandy family _without anything to show for all the shit you put us through?_ ”

Gaster didn’t reply. He had completely frozen, not a blink, not a breath, not a twitch, his eyelights shrunk, and for a second, just a _split second,_ Sans saw something like pain flash in the backs of those sockets.

Then it was gone.

Gaster lowered his gaze.

“Sans, stop it.”

“ _me_ stop it?” Sans spat, taking a step toward him, his smile stretched in a scowl. “how about _you_ stop it? how about you just _stop_ all of this? do you really see this going anywhere? do you _really_ think any of this has a point?”

“You’re getting stronger,” Gaster muttered, and it was cold and scientific and factual and so quiet Sans wasn’t even sure he believed it himself.

Sans’s browbone lowered. “didn’t you just say i was getting _weaker_? ”

Gaster paused, just long enough for Sans to catch the hitch in his breath. He shifted his gaze to the side.

“But your _soul_ is getting stronger,” he replied, so calm, why did he have to be so _calm_ about this? He let out a soft breath. “We haven’t done a soul-endurance test in a while. We could be getting close. As soon as your soul becomes similar enough to a human’s, once we can confirm it, we can extract this human’s soul and give it to you. Then all we have to do is tell the king and get the other five and I’ll get us out of here.”

He looked to Sans again, and Sans swore the S.E. coursing through his bones started to boil.

“ _You’ll_ get us out of here.”

And he sounded so proud, so hopeful. A tiny smile twitched at the corners of his mouth, it was barely there, but Sans could see it, he could always see it, he could see every minuscule hint of the man who used to be his dad, and he hated it but every time he could feel his own soul grow warmer, clinging to the smallest possibility of all of this _ending._

Gaster looked at him, so soft, so warm, and Sans had never wanted so badly to die.

“Then everything can go back to normal, Sans,” he said, and that was his voice, that was his dad’s voice, he stood there like he had stood there so many times, like he could pull Sans into a hug at any moment, like there wasn’t a human unconscious on a table across the room, like Sans didn’t have a human’s blood in his bones, like Papyrus wasn’t back at home curled up in his room because he had lost _everything_ he cared about. Gaster smiled wider. “Everything you want. Everything you keep reminding me of. Just a little longer, and we can have all of that back. We can have dinner together, play games, we can go out in town, we can go out and watch the stars together and Papyrus can finally drive a real car and—”

Sans didn’t even feel himself summoning the blaster before the beam was shooting across the room.

Light.

Blinding, overwhelming, even more so than before.

Then … silence.

And Gaster, standing exactly where he was before, his lab coat barely shifted out of place.

Sans stared at him. Gaster stared back. Neither of them spoke for a good ten seconds. Sans’s arm remained in the air, shaking even harder before he forced it down again. His breath trembled, his bones burned with the foreign material within them, and he had never in his life felt less like himself. And Gaster stood there, yards away from him, in the direct path of the blaster, with only 3 less HP.

The hint of a smile had faded from Gaster’s face, and Sans hated himself for missing it.

“You’re becoming irrational, you know,” Gaster went on, huffing a sigh and shaking his head in disappointment. “We just tested this. You know how low your output has become. I would have thought you were sensible enough to at least choose a method of attack that—”

His voice cut off with a jolt and a cringe, his teeth clenched and his eyes widening.

And his HP dropped 3 more points.

His body froze. His teeth parted, though no air came out. And Sans just stood there, all but gawking, his arm finally dropping back to his side.

He hadn’t hit him again. He _definitely_ hadn’t him again. He _wanted_ to hit him again, he would have gladly blasted him right out of the room, but …

He hadn’t done anything. He had just been standing there. And Gaster’s HP had gone down even further.

Sans’s eyes locked on Gaster’s face, and after a few seconds, Gaster’s own gaze returned to him, sockets wide, mouth still open, the rest of his body motionless.

For the first time Sans could remember, when Gaster looked at him, he swore he saw fear.

Then Gaster looked away.

“That’s enough for today,” he bit out, quieter, faster, than Sans had heard him in weeks. “You can go home now.”

“And what if I wanna stay?” Sans asked, trying to meet Gaster’s eyes, but failing every time as Gaster kept his own gaze firmly on the other side of the room.

“I said you can go home now,” Gaster snapped. Sans tensed, but said nothing. Gaster paused, then let out a long, heavy sigh and started across the room. “I have work to do. I don’t need any distractions.”

Sans shouldn’t have felt a sting at the implication that he was a distraction. But he did anyway.

He stood there for a minute, watching Gaster go back to checking machines, making notes, as if Sans wasn’t there. He didn’t seem to be doing anything in particular. Maybe he was just trying to pass the time until Sans left. A part of Sans wanted to see how long he could stand there before Gaster forced him out. But the rest of him was tired. The rest of him just wanted to go home.

Even though there wasn’t much of a home to go back to.

He turned around, allowing himself a brief glance at the unconscious human on the table before he forced his eyes ahead, on the door. But as he walked forward, he found his gaze drifting toward the table near his “injection chair,” covered with at least two dozen different random items Gaster had dropped there over the past few days.

As well as a large, curled up piece of blue paper, which had been sitting in the same spot, forgotten, since yesterday.

Sans had never spent much time looking at the blueprints for the extractor. He knew they were there, and he had glanced at them in passing, but he didn’t have a _reason_ to read them. Gaster didn’t have a reason to read them. He had consulted them when he was making a few adjustments to the machine, and just never put them away in the drawer where he had found them, gathering dust after decades of disuse.

There was no reason for Sans to care about them. It wasn’t like he was going to build another extractor, after all. But he still found his eyes flicking across the room, to where Gaster had now begun to examine the wall in earnest, jotting down notes every time he found a new mark.

Before he had a chance to turn around, to notice that Sans had stopped moving, Sans picked up the blueprints and shoved them, as quietly as he could, down into his bag, before picking up the bag and flinging it over his shoulder.

Maybe it was pointless. Maybe it wouldn’t do him a bit of good.

But it felt better having them than not.

He risked another glance at Gaster. Still distracted. He had gotten used to ignoring him. Sometimes Sans wondered if the sixth sense that made his dad notice even the smallest whimper when they were kids had somehow transferred to his research, and Sans and Papyrus could have stood behind him, screaming and waving their arms, and Gaster wouldn’t have blinked.

But he didn’t need to scream and wave his arms. The old Gaster would have noticed the slightest of movements, but this Gaster either didn’t notice or didn’t care. And that was all Sans needed.

With practiced ease, he swiped the half-empty bottle of S.E. from the counter and slid it into his bag alongside the blueprints.

Still, not even a twitch.

And even though it was stupid, even though it was absolutely idiotic, Sans couldn’t help but feel his soul twist and ache when he walked out of the lab with his stolen supplies without Gaster sparing him so much as a glance.


	36. Chapter 30

**Notes for the Chapter:**

> To those in America who celebrate it, Happy Thanksgiving! I'm grateful for all of you and ... this chapter is a terrible way of showing it. XD

It was getting harder and harder to get away without attracting Gaster’s attention.

Not that Gaster had been paying much _attention_ to him when he wasn’t being injected with S.E. or examined after an experiment. But the experiments, combined with the “work” done on the human, were taking up so much time that when Sans did get a free moment, all he wanted to do was collapse and sleep until he died. Sometimes, he did sleep, though rarely for more than two hours at a time. The rest of the time, he pushed his own exhaustion to the back of his mind and dragged himself to the lab anyway.

He didn’t need to think about where he was going, and usually, he didn’t. He could have walked there with his eyes closed and probably not run into anything on the way there. That wasn’t to say he _didn’t_ run into anything, but that was usually because he was dizzy from the weakness that seemed to increase by the day, despite the apparent “strength” he was gaining from the injections of S.E. Sometimes he wondered whether Gaster’s definition of strength was the same as his. Sure, he had new attacks, potentially very strong attacks, but he had no energy to put strength _into_ them, and when it came to walking from one part of the underground to another, he was about as useful as a babybones.

Still, though, if he managed to push himself to _start_ toward the lab, most of the time, he made it. Today, he made it, though not until almost five in the afternoon. Once, he might not have felt like it was even worth it to go to the lab that late, but it wasn’t like he would be eating dinner with Papyrus anyway. Or reading him a story. Or talking to him at all.

It wasn’t like Papyrus would talk back.

He could spend several hours here, get some real work done, before he had to get home.

He stopped in front of the door, not even bothering to glance around to see if anyone was watching. Hadn’t that been important before? He wasn’t sure now. He dug his hand into his pocket and pulled out the key, sticking it into the lock like he was stabbing it with a knife.

At the slight force, the door slipped out of place in its frame. Bit by bit, it creaked open.

Sans froze.

He … hadn’t he locked that door? He had, he was sure he had, but … he closed his eyes and hissed. He was doing it again. Did he used to forget stuff this much? He was supposed to lock this door, he _always_ locked this door, he thought it had become muscle memory by now, but …

Whatever.

He pushed the door the rest of the way open and stepped inside. Everything was still there, just as he had left it. Probably. Maybe he was forgetting what it looked like before. In any case, the machine was still there, just as all of his other supplies, at least the most obvious ones. He didn’t know what anyone would want to steal from here anyway. Stealing wasn’t common in the underground, and why the hell would anyone want to steal a bunch of scientific equipment in the first place?

He was being silly. Paranoid. Had he ever been paranoid before? Had he had a _reason_ to be paranoid before? He had heard horror stories of scientists stealing one another’s work, but it was even more rare than literal stealing, from what he understood. There seemed to be a silent agreement among the small monster scientific community that claiming ownership of someone else’s work was even more shameful than never having created anything of worth at all.

And anyway, it wasn’t like he gave a damn if someone else somehow replicated his machine.

It wasn’t like it would make a difference.

He set down his bag and dug around inside, pulling out the small glass vial he had tucked in the bottom before he left the lab. He lifted it in front of him, watching the thick red fluid slosh around inside. It still looked so much like human blood. Not that he was an expert, but seeing it every time they draw it from the kid’s arm, seeing it go into his _own_ arm as a “precautionary measure” … it made enough of an impression to last.

He knelt down in front of the machine, pulling open one of the panels to get to the inner workings. He had to dig through the wires a bit to get to the glass orb in the center. It was smudged and close to cracking in places, but it held as he plucked it out and unscrewed the top. Balancing it on his leg, he uncapped the vial and watched the thick red liquid slip down to join the liquid already settled inside. As soon as the last drop fell, he capped it again, set it aside, and leaned in close to return the orb to its spot behind the wires.

He wasn’t sure where he had gotten the idea. His mind wasn’t working right nowadays, and sometimes he didn’t know where his own thoughts came from. He didn’t even know why he had snatched the vial of S.E. in the first place. But once he had it, he couldn’t think of anything else to do with it, and he wasn’t about to leave it sitting around—or give it back to Gaster.

So, without any reason he could name, he had poured the S.E. into a little round container and stuck it inside the machine, hooking it up to a few of the main systems.

It was a stupid idea, now that he had time to think about it. They weren’t even sure what S.E. was doing to _him,_ why would he think it would do anything for the machine? And it wasn’t like the S.E. had anywhere to _go,_ it would just sit there. Useless. But nothing else he did was working, and besides, it was still in a separate container, and if it screwed something up, he could just take it out.

But it didn’t screw anything up.

He wasn’t really sure _what_ it did, but it wasn’t making it worse. And that was enough motivation for him to keep trying.

So he snuck more of it. And more. And more. Every day, when they were done extracting the S.E., before or after they did the other experiments, Sans slipped a little bit of it into another container he carried with him. It wasn’t very much, but he would have thought it would be noticeable. But apparently Gaster was too focused on the other aspects of his research to notice that the amount he added to the storage unit was a little smaller than it should be.

Too focused, even, to realize how stupid it was to give Sans control of the S.E. in the first place.

Sans kept working on other aspects of the machine, of course, but every day he came by, if he had any more S.E., he added it in. Maybe it was silly. Maybe it was stupid. Maybe it was a waste of time. But at this point, he would take any chance he could get, and with all that S.E. had shown itself capable of so far, he was willing to cling to the hope that it could do something here.

And it was.

Sort of.

It wasn’t making it worse, and it didn’t seem to be making it _work_. But that didn’t mean there wasn’t a change.

Sans … just didn’t know exactly what that change _was._

He hadn’t paid much attention to the aspects of the T.F. machine that had survived within his new machine. Maybe it was his subconscious’s way of guilting him for tearing up a machine that had taken Dr. Billington years to design and build, probably the greatest work of her entire career. Or maybe he had just been focused on something else.

But he was fairly sure that the readings in Alphys’s program had been stable before he began adding the S.E. to the machine.

And after he began … something changed.

It wasn’t a regular change, not like the sort of changes he might have expected from some fluctuation within the other universes. Or at least … he didn’t think so. Once Alphys had figured out that it _was_ parallel universes causing the discrepancy in the readings, he hadn’t thought much about the specific numbers. Not unless they could teach him something about the universes in question, which, at the moment, they couldn’t. It wasn’t a huge change, either. He might not have noticed it if he hadn’t already been paying such close attention.

But this was different than any of the changes he and Alphys had studied before. When he tried to pull this up in her mapping program, it didn’t work. It mapped out the readings for the usual timelines, but there was something … off about it. At the same point in all of the timelines he could read, something seemed different, and he couldn’t figure out what the hell it was. It didn’t follow the behavior patterns of normal spacetime readings, like the parallel universes had. The numbers went up and down, stayed fixed and fluctuated like crazy. It left him even more stumped than he had been months before, when this whole mess had begun.

The only thing he could determine was that it seemed to be focused on this spot in physical space. It was almost impossible to pinpoint something like that in a machine that measured timelines, and he couldn’t exactly move part of the machine to take the readings somewhere else without moving the rest. But whatever had happened, it was fixated here, around the machine.

And it hadn’t been there before he began adding the S.E. to the machine’s core.

Maybe it wasn’t getting him in the direction he wanted to go, but it was doing something. And at this point, any sort of progress was worth pursuing, even if it turned out to be useless in the end.

Besides, less S.E. in Gaster’s hands meant less S.E. that went into him.

Of course, he really couldn’t care less what happened to him right now. He could deal with the pain. He could deal with the side-effects. But he had to be able to come to the lab. He had to be able to get his work done. And just like the S.E. was affecting the machine—in whatever twisted way he had yet to define—he was sure it was affecting him as well.

He was tired all the time. Maybe that was because of the experiments, or maybe it was just because of the exhaustion of going to the lab and watching a human kid being slowly killed in front of him. Or coming home every day to the reminder that his brother still wouldn’t speak to him, that he had screwed everything up, that his mistake months earlier had wrecked every good thing in his life. Sometimes it was a miracle he managed to drag himself out of bed in the morning. His vitals were stable. Gaster made sure of that. He wasn’t dying. But he wasn’t thriving either.

And last time he checked, his HP was down to 2.

He hadn’t checked it much lately—only once or twice since Gaster brought it up. It wasn’t dropping at a truly alarming rate, even if it _was_ still dropping. He moved a little slower throughout the day, his thoughts a little more sluggish, his bones a little less willing to carry him out of bed in the morning. Sometimes he thought the S.E. was making it worse. Sometimes he suspected it was the S.E. that got him through the day.

Papyrus had noticed, of course. Or he probably had. He still didn’t say anything to Sans when he came home in the evenings. He looked at him, when he came out of his room, and Sans knew Papyrus watched him when he thought he wasn’t looking. But he never spoke.

When they were eight, Sans had joked that Papyrus couldn’t stay quiet for an hour unless something was holding his mouth shut.

Maybe if he actually managed to go back in time, he could find a way to punch his eight-year-old self in the face.

Then he found himself trying to remember what his eight-year-old self had been like. What it had felt like to be so hopeful, despite the regular disappointment when his dad came home late or not at all, when he realized that the stars he had spent so long dreaming of would always remain out of his reach, and he knew it was time to move onto a field he could actually _do_ something in. He had never given up, even when things were tough.

He couldn’t imagine what that felt like now.

He didn’t feel like that kid anymore. He didn’t feel like _him_ anymore, or he didn’t feel like Sans, or the Sans now didn’t feel like the Sans he had been then. He had changed. Slow enough that he didn’t notice it happen but so quickly when he really thought about it.

He didn’t know when it had started, and he didn’t know when it would end. If he went back in time to meet his past self, would he even recognize him? He had questioned, once, whether he would stay in the past himself or get rid of his past self to avoid a paradox, but now it wasn’t even a question. If he stayed in the past like this, he would just screw things up. He wasn’t him anymore. He wasn’t the Sans he wanted to be. He wasn’t the Sans Papyrus needed, not the Sans he _deserved._

He was a coward. He knew he was a coward, he knew he had chosen the easy way. But he still couldn’t go back on his choice. He couldn’t risk the chance of his brother being hurt again. He would allow a thousand humans to be tortured if it meant keeping Papyrus out of danger. Papyrus hated him for it, or as close to hating as Papyrus ever got. But Sans still couldn’t bring himself to change his mind.

Gaster had wanted to make him more like a human. He had wanted to find every way he was similar to a human and amplify it. He had tried that with Papyrus, and he had failed.

But Sans wasn’t Papyrus. Sans wasn’t so infinitely compassionate and hopeful.

Sans was probably a whole lot more like the human strapped to a table in the lab than even Gaster could imagine.

And he wasn’t even sure if it had been the S.E. that made him that way in the first place.

He stayed in the lab for a couple of hours after that, tinkering with the machine, even though there was very little he could do now that would actually make a difference. Aside from the S.E., he had hit a dead end. Even when he had first started this, he hadn’t had a specific end point in mind. He didn’t know _how_ he was going to build a time machine. No one had ever built one before, and he had known that most of his work would be experimentation. And he had known—as he did now—that actually testing the machine was a whole new risk on its own. If he tested it and it just flat-out failed, then he would keep going, but if he tested it and it worked partially, maybe throwing him into some random time period or into some no-man’s-land or just exploded and killed him …

He would have to test it eventually. But he couldn’t help but want to try as many things as possible before he did.

Once he started trying it, for real, there was no going back.

And he would have to risk just dying and never fixing anything, in any universe, in order to figure out if it worked at all.

But he could wait a little longer.

He still didn’t know all the differences the S.E. had made, after all, and he could at least figure that out first.

He didn’t know how late it was when he left the lab. Most people had apparently gone back home already, and it was a bit darker than before, though it was hard to tell given how dim Waterfall usually was. He started to turn back toward his house, just like he did every other evening, but found himself pausing. Before he could think, his feet turned him around and started him off in another direction. It took him less than a minute to realize where he was going.

He could have stopped. But he kept walking anyway.

It took him less than ten minutes, even going as slow as he was, to get there. He hadn’t really thought about how close it was to his lab before. But that was why he had been there, wasn’t it? He had finished work early and decided to go by the Signa shop, see if they had any new clothes he could pick up for Papyrus. Then the ceiling had started rumbling and they were all rushing outside to see what it was and before they had time to move the rocks were falling and they were crushed, suffocating, _dying,_ not dying, they were fine and the rescuers were there and the healers had done their work but his dad …

His dad …

He stopped in front of the pile of rocks, taking a few seconds to figure out what would have been in front of him if he had come here months earlier. He had seen the shop dozens of times, _hundreds_ of times, he knew what it should have looked like, but it just … wasn’t there anymore. Would never be again. The Signa family had moved on, found another home, from what he had heard, though it wasn’t like he had been keeping track. No one would live here again, even if they could find a way to move the rocks. No one would dare live here after what had happened. Even a few families who had lived nearby had moved, apparently, unwilling to risk being victim to a secondary rockslide.

It was a small area. There were much more densely populated places, even in Waterfall. It could have been worse. It could have been much, much worse.

But that didn’t mean it wasn’t already bad.

This had been a part of his childhood. A part of his life. One of the best clothing shops around, with one of the friendliest families he had ever met. And there was nothing left of it. This part of their world had been cut away, and they would never get it back.

He looked up, toward the ceiling, the crater from before now settled, but just as deep as it had been after the initial rockslide. There were no holes letting in sunlight, as he might have hoped, if he had been prone to hoping for such things. No glimpses of what life they might have. Just more instability. He was hardly a geology expert, but he doubted that having a giant crater in the ceiling did anything to make their home more stable than it already was.

The humans had done that.

That was what he had heard Gaster saying, at least. And it made sense. If the mountain had held for thousands of years, why would it suddenly collapse like that? It could have just been a geological phenomenon, rock wore away over time, but … it had been so sudden. And based on the murmurs he had overheard among the older monsters, it had never happened before.

Did they know they were down here? That human had said that she didn’t know anything about monsters. Maybe the younger ones didn’t but the older ones did. Or maybe … it had been two thousand years, hadn’t it? Did they not know that there were people trapped down here? People _they_ had trapped down here? Did they have any idea what they were doing?

Did it matter?

Did it change the fact that the Signa family had lost their house and their shop in a rockslide? Did it change the fact that all of their home had gotten just a little bit smaller?

Did it change the person his dad had turned into in his desperation to get them out?

Would he have turned into that anyway, given enough time, if the rockslide hadn’t happened at all?

It still came back to the humans, though, didn’t it? If the humans hadn’t trapped them down here in the first place, none of this would have happened. Would he and Papyrus even exist, if the war hadn’t happened, if the humans hadn’t won? Did that make the humans responsible for creating his life as well as ruining it?

Would it have been worth it, to not exist at all, if it meant that monsters had never been trapped down here?

If it meant his dad was still …

He hated them. He hated Gaster, and he hated the humans, and he couldn’t even decide who he hated more. Maybe … maybe that kid deserved what was happening to her. Maybe … he didn’t know what she had done. He didn’t know what kind of person she had been, before she fell. He didn’t know what kind of person she could have turned out to be, if they had let her go.

She had pointed a gun at them, after all.

He felt sorry for her, but why should she? If that was what humans were like, if that was what _all_ humans were like, then didn’t they deserve whatever they got? Didn’t they deserve to die for the barrier? Hadn’t he always thought that? He had always assumed that if a human fell, it would be captured, killed, its soul taken to help break the barrier, but he hadn’t really _thought_ about it. Not when he considered all that implied.

Not when he considered what his dad had done to the last human who had fallen down here.

He had been okay with that before. He had been okay with it in theory. But seeing it in person, seeing it when the same damn things had already been done to _him_ …

He didn’t notice his hands curling into fists until they began to tremble, and he forced them to smooth out. He looked at the pile of rocks, at the debris, at the remnants of one small part of the underground that had once been so familiar to him.

It didn’t matter now.

The experiments on the human would finish, eventually, and then it would be killed. Then its soul would be collected and they would only need one more.

And maybe … if Gaster’s experiments worked … that one more would be taken care of.

But … then he wouldn’t get his dad back.

If he let Gaster continue, the barrier might really be broken. But if he went back in time, if he fixed it, like he had wanted to … they would lose the progress they had made. Even if it was progress he hated, it was still progress, and he would set them back two souls. He would push everyone back years, decades, maybe even _centuries_ from getting out of here.

Papyrus would be happy. Happy that the human was safe. Happy that their dad was still their dad.

But … it wouldn’t even matter, would it?

 _This_ Papyrus would stay here. Sans would just abandon him, and go back in time to save their dad in some other universe and then kill himself so he wouldn’t cause a paradox. He couldn’t go back to his own universe, once he created a new one. He would just be creating a new one so that somewhere, _somehow,_ his family would be happy, even if he never got to see it.

He was abandoning them.

He was abandoning everyone.

And maybe this Papyrus would get to see the surface but he wouldn’t _want_ to and his dad wouldn’t be the same and Sans wouldn’t even be there and … and …

Sans gritted his teeth and squeezed his eyes shut.

No. _No._ He had come this far. He had worked this far. He had to do it. He …

… That was what Gaster would have said, wasn’t it?

_We’ve come this far already, we can’t quit now._

He _could._ He could quit and focus on his brother and try his damnedest to fix everything right here, even if he knew it would never work. He could give up on one thing, he could focus on another. He could stay with his brother. _His_ brother, this version of him, broken and scared and alone but _maybe Sans could still help him._

Even if their dad was never the same.

Even if …

He opened his eyes and bit back a trembling sigh.

Later. He would think about this later.

For now … he just needed to go home and rest.

He would think about this tomorrow.

He turned around and started away from the rubble, back in the vague direction of Hotland.

“Sans?”

Sans stopped.

He knew that voice. He _knew_ he knew that voice, but it still took a few seconds for him to recognize it. How long had it been since he had heard it? It couldn’t have been that long, and he had heard it all the time, almost every visit to the lab when he was a kid, every time she babysat, every time she came over to make sure they ate dinner or had someone to tuck them in.

He turned to his left, allowing himself one long blink as his eyes fell on her, standing only a few yards away.

“dr. japes.”

He didn’t know how she had managed to approach him without him hearing. Or … well, it wasn’t like it would have been that hard. He had been missing all kinds of things lately. It only made sense that he would miss something like this, too.

Either way, no matter how long she had been standing there, watching him, she was here now. Staring at him with those same soft eyes he had memorized for as long as he could remember.

“Sans …” she breathed, taking a step closer. Her mouth curled into a hesitant, vaguely sad smile. “It’s been a while.”

“Yeah,” he murmured, forcing his voice a little louder than it would have been otherwise.

She looked upset. Why did she look upset? Had something happened? What did she have to be sad about? Everything was fine with her, wasn’t it?

She took another step forward, her lips pursed into a tight line.

“I was just … going for a walk, I didn’t know you’d be … it’s good to see you. I’ve seen you coming to the lab a few times. With your dad,” she began. Something twitched in Sans’s head. Her eyes softened further, in something like sympathy. “Dr. Lemming told me your dad … found a human.”

Oh.

Right.

He didn’t pay attention anymore when he came to the lab, or when he left it. For all he knew, he could have passed her a dozen times over the past few days. It wasn’t like she had stopped working there, after all. Or Dr. Lemming. Or Dr. Frewth. They were all there. Every day. Every day, the human screamed, every day, they did more experiments, every day he went through hell and they were _right there down the hall and they didn’t know they didn’t do anything they didn’t—_

“Do you … have things been … you haven’t been hurt at all, have you?”

Sans jolted, and for a second, his soul stopped. His mind had already run through about twenty different possibilities as to how she had found out—and what the hell he was supposed to do now—when he took a second to really look at her.

No. She didn’t know.

If she had known, she wouldn’t be looking at him like that. She wouldn’t be looking at him like she was worried, concerned, sad, but like … like this was something that had to happen.

She wouldn’t have wanted this to happen.

She wouldn’t have _let_ this happen.

She would have stopped it. She would have stepped in if she knew, if she had any idea, she wouldn’t have let it get this far, if he had just told her, if he had grabbed Papyrus and chased after her after he found his brother in that damn lab, she could have stopped all of this, she could have—

He swallowed and shook his head.

“no,” he muttered, barely louder than a breath. “we’re fine.”

He didn’t really expect her to believe it, and he wasn’t sure if it was relief or anxiety twisting his soul when his expectations were confirmed.

“Based on my experience with the last human who fell, I sincerely doubt things are ‘fine,’” she replied, but gently, just as gently as she had always spoken to them. Even when they were in a bad mood. Even if she was mad at their dad. Even if everything else in their life was going wrong, she was still there. Stable. Like a rock. She closed her eyes and sighed, shaking her head. “None of this is … I wish you didn’t have to go through this, Sans. And if you don’t want to participate, you don’t have to, you know. I never … I wouldn’t have thought Dr. Gaster would even _want_ you to participate in this research. Haven’t you been working on some things on your own? Readings with the T.F. machine, wasn’t it?”

Sans started to reply, before finding that he had no idea what to say. For a second, he couldn’t even remember what she was talking about. It took him at least five seconds to remember what he had been working on before all of this had started. To remember when the T.F. machine had actually _been_ the T.F. machine, and not some bastardized contraption he had thrown together in the vain hope that it would fix all of this.

To remember when it had seemed so exciting, rather than so desperately important.

He took a step back.

“look, I … i’ve got some stuff to do. It was good seeing you, but I … I’ll see you later.”

He turned around before she could respond, already lifting his foot, ready to walk away as fast as his feet would carry him.

“Sans.”

He stopped. He tried to make himself move, but his body had frozen, his teeth gritted, his eyes wide. Dr. Japer didn’t step any closer, and he didn’t need to look at her to imagine the look on her face as she sighed.

“Alphys called me.” Sans said nothing. Dr. Japer took one step, then stopped again. “She wouldn’t tell me what was going on, or any of the details, but she said … there was something wrong. And she didn’t know how to help.”

Sans wanted to run. Damn it all to hell, _why wasn’t he just running?_ It wasn’t going to help him to hear this, it wouldn’t change anything, it _couldn’t_ change anything, but still he found himself turning back around, god, he didn’t want to see her face but now he could and it just made it worse but he couldn’t look away.

“She’s worried about you,” Dr. Japer went on, her eyes so soft, so caring, so _genuinely concerned and he had almost forgot what that looked like._ “And so are Dr. Lemming and Dr. Frewth. And me.”

Sans tried to look away, but he couldn’t. He couldn’t move, he couldn’t breathe, his chest burned and his eyes burned but he wasn’t going to cry, he didn’t have any tears left, _tears had never helped anyone and they wouldn’t help now._

“We almost never see you or your dad anymore, and Papyrus is never out in town, no one sees any of you. I know that I’m not … technically your family, but …”

She trailed off, glancing off to the side. She was so much older than him, but she looked so young, so vulnerable, she had been there from the beginning and for a second all he wanted to do was comfort her, say that it was alright, even though it wasn’t and he knew he couldn’t lie. Then she looked back and he froze again, staring at the pain glimmering in her eyes.

“Sans, I hope that after all this time, you know how I think of you. And Papyrus.” Her lips curled up into the beginnings of a smile, and she took a few more slow, careful steps forward, until she was only a few feet away. “You’re like … you’re like two more nephews for me. Lin always loved it when you two came to visit, you’re like his older, fun cousins.”

“dr. japes …” Sans breathed, his sockets as wide as they had ever been.

Another step. She straightened, her eyes desperate, aching, so determined to fix this, just like she had fixed everything.

“What can I do, Sans? Please, I want to help, but I can’t help if you don’t tell me what’s going on,” she said. She stepped closer still. “Whatever’s happening, we can fix it. Whatever you’re going through, we can get through it together.”

He tried to talk, he _wanted_ to talk, but he couldn’t, and all he could do was shake his head and make vague noises as his voice tried to escape his throat even though there was nothing to say.

She held her arms out for him, and it took every ounce of his self-control to stop himself from collapsing into her embrace, letting her hold him, rock him from side to side, pet his skull like she had so many times when they were little and their dad had no idea what to do and she took over, just for a little while, she wasn’t a replacement, she wasn’t his dad, but she was _good_ and she cared about them, she loved them, she wanted to help them, she wanted to help them now, and she _could,_ all he had to do was tell her what was going on and maybe she could—

Her hand touched his shoulder, and he jerked away so fast he almost fell over.

No. No, no, _no,_ he had come this far, he was getting close, he could feel it. If he told her now, everything would be ruined. She would get his dad arrested and she would want to take them in, what if she didn’t give him the freedom to work on his machine, what if she didn’t give him the _chance_ to go back and fix everything?

And … the S.E., it was helping. He hated it, but it was doing _something_ and whatever that something was needed more S.E., it was painful, Papyrus hated him and he was miserable and he wanted all this to end but he was moving _forward,_ he couldn’t just give it up. Not now. Not after all this.

Not after all he had already lost.

Dr. Japer’s hands pulled back, gently, but she didn’t step away. She looked at him with such soft eyes it hurt, why did she have to be so affectionate, why did she have to _care_ about him?

“Sans …” she started. She opened her mouth again, ready to continue.

But Sans shook his head, taking another few steps back, cutting her off.

“i need to go,” he said, his voice tight and breaking.

She reached out toward him again, but before she could take a step forward, he turned around and ran.

He didn’t look back, and he didn’t stop until he got back to the house.


	37. -9

**Notes for the Chapter:**

> We're about to hit the last major plot arc of this story ... any theories as to what's going to happen? ;)

Sans was upset.

He had never been quite as open with his feelings as his brother, but he had always been expressive enough for Gaster to know when something was wrong. Sans never stopped smiling, technically, but anyone who had known him for a few days could tell when it was real, and when it was just a biological fact he couldn’t control. And now, even though he had just talked in the door, Gaster was sure that Sans was upset.

He just didn’t have any idea what to do to fix it.

It was ridiculous. His sons were ten years old. He had had a _decade_ to get to know them, to understand them, he had been there for all the important moments in their lives, but now, looking at Sans slumped over at the corner of the couch, he still found himself coming up blank.

He set his bag down and closed the door behind him. Sans didn’t even glance up. Gaster furrowed his browbone. He knew both of his sons missed the days when he could pick them up from school, but … he had thought they had gotten used to it by now. At least, they hadn’t complained about it. Maybe it had been bothering them and they just hadn’t said anything? Maybe something had happened at school? Was it something Gaster did? Was it something he could fix?

Was Sans upset that Papyrus wasn’t here tonight?

That might make sense. It was the first night in his entire life that he wouldn’t have his brother nearby, after all. Papyrus had been invited to a sleepover, and even though he didn’t know the other kids very well, he had immediately begged Gaster if he could attend. Gaster had been … hesitant, not because he didn’t trust Papyrus, but frankly, the idea of him _not_ being at home overnight made Gaster more than a little anxious. But he wasn’t about to turn down his son when he was so excited about something, so he had simply smiled, nodded, and texted the other child’s parents to ensure that plans were settled and that they sounded like decent people.

He had met them once, he was fairly sure, even if he couldn’t remember what they looked like, and they knew him, if only because _everyone_ knew him. They were nice, and they seemed fond of Papyrus already. So last night, Gaster had helped Papyrus pack an overnight bag to go along with his backpack, and he had received a text while he was still at the lab from the other child’s parents, ensuring that Papyrus had been picked up along with all the other kids and would be returned home around eleven the next morning.

Gaster was happy. But he was still anxious.

And if he was anxious … well, it would only make sense that Sans would be, too.

Now it was just a matter of figuring out exactly what about it had upset him, and how to get him to admit it when he didn’t exactly seem to be in a talking mood.

Gaster took a few steps closer, slow, careful, stopping a couple of yards away from the couch. Normally Sans would at least look at him when he got close. But today, he didn’t even seem to notice him. Gaster frowned, clenched his teeth, took a deep breath, and cleared his throat.

“How was school?” he asked.

Sans shifted his face a little further toward the cushions, his expression unreadable.

“Mm.”

Gaster frowned. “Is that a good mm or a bad mm?”

“Mm.”

Gaster’s fingers twitched, and his chest ached. This really was ridiculous. He knew they didn’t talk as much as they used to, as much as he _wanted_ them to, but usually he at least had a clue as to what was wrong. He paused, wracking his head.

“Did you get to see Papyrus at school before he left for the sleepover?”

Sans shrugged without looking up. “At lunch.”

Another pause. Gaster shifted.

“Are you … disappointed that you aren’t going, too?”

“No,” Sans answered, without hesitation, but not so quickly that Gaster would suspect he was trying to cover something up. “I don’t know those kids.”

Gaster resisted the urge to bash his head into the closest wall. Well, if Sans wasn’t going to tell him what was wrong, he would just have to figure it out on his own. He had designed the Core, he had built some of the most complex machinery in the underground, he was widely considered one of the most intelligent monsters alive.

Yet somehow this problem seemed infinitely harder to solve.

But this was his son. He knew his son, even if he didn’t spend nearly as much time around him as he would have liked.

Anxious. That had been his first theory, hadn’t it? Maybe Sans was concerned that things wouldn’t go well at the sleepover. After all, Papyrus was no stranger to bullying, even if things had gotten a good deal better over the past few years. In most cases, Sans had been there to stop the worst of it, or at least fight back or tell a teacher when Papyrus refused. But now … maybe Sans thought that the other kids were just luring him in to play a cruel joke on him. Maybe he thought this was just another ruse to make fun of him for the many ways he was different from the average child.

It wasn’t like the thought had never crossed Gaster’s mind.

But he stopped himself before the thought could overtake him, and took another step closer to the couch.

“I’m worried, too,” he said at last, forcing his voice into some semblance of calm and reassurance even as he pleaded to the stars that he had made the right guess. He managed a small smile, though Sans didn’t turn to see it. “But … I think he’ll be fine. And I told him not to hesitate to call if he wants to come home. We can always pick him up if something goes wrong and he doesn’t want to stay.”

“Mm,” Sans replied.

The wall was looking more and more attractive by the second.

He should have been home more recently. Of course, he should have been home more in general, but with everything shifting around as it had been in the past year, it was even more important than before. Sans needed him. _Both_ his sons needed him, but Sans … he had been going through far too much life turbulence for a ten-year-old to deal with by himself.

The science fair had changed things—or maybe things were ready to change anyway, and that had just been the moment that marked the end of one era of their lives and the beginning of another. The school had called him in for a private meeting, and he had been told, for perhaps the five hundredth time, that his son was far above average in intellectual capability. He had known that, of course, even before the boys had started school. But this time, his teachers insisted that while Sans got along well enough with his classmates, he seemed socially maladjusted, and got along far better with the older kids—which were getting difficult to find, given that he was nearing the end of elementary school and most of the kids not his age were younger.

On top of that, it was getting nearly impossible for his teachers to work with him on his advanced studies while still teaching the other kids. Sans was self-motivated and rarely needed help, but when he _did_ have questions, it was usually about something even his teachers knew very little about. He was already pushing the edges of what high school could offer.

Once again, they brought up the idea of moving him ahead officially, so he could interact with older students who could more easily hold a conversation at his academic level.

And this time, when Gaster brought it up to Sans, he agreed.

Not immediately, of course. He spent a few days giving it some thought—and really, he could have taken all summer, if he liked, given that he was already finishing up third grade and it would have been pointless to skip him ahead so late in the year. But he only took four days total before he told him that he would give it a try.

He didn’t like the idea of leaving Papyrus, in any sense of the word. But they hadn’t been spending as much time together at school anyway—they were in different classes, and had been for the past few years, and besides, they were learning completely different things. They were as close as they had ever been, but Papyrus had settled in far more than he had back in kindergarten, when Sans first turned down the idea of acceleration, and he agreed on the condition that he could go back if things didn’t work out, and that he would still get to cross the short space between the schools every day to eat lunch with his brother.

The two of them were still best friends. Brothers. As much as they had ever been.

And they needed it, with how little time Gaster had been able to spend with them over the past few months.

Even though the temperature stabilization mechanism had changed things for Sans, and even though it had been a tremendous help in the advancement of the Core, it hadn’t solved all of the problems Gaster had run into. It _stabilized_ the temperature, certainly, but the temperature was still much too high. The metal in certain parts of the Core had already shown signs of melting, and though so far they had been able to make do with replacing it every once in a while, it wasn’t a feasible solution in the long run. Which meant far more late nights and weekends trying to come up with a long-term fix, something that would keep the Core going without needing replacement parts that didn’t exactly grow on trees around here, something that would allow the Core to function without Gaster there every day to monitor it. He had other things in his life he needed to focus on.

On top of that, as old as he was, as long as he suspected he still had to live, he wasn’t going to live forever. The Core had to be able to work without him around to maintain it.

And as much as Sans would have done a spectacular job of it, he wasn’t going to put that responsibility on his son.

Not when he had so many other incredible things ahead of him that had nothing to do with his dad’s old projects.

He tried not to talk to Sans about it—even though he was sure his son had figured out what was going on by now. He was observant like that. But Gaster still did his best to keep his worries to himself, encouraging Sans to focus on finding his own favored areas of study. Just because he wasn’t going to go into astronomy like he had hoped didn’t mean he hadn’t found plenty of other areas he enjoyed. Physics, at the moment, was right at the top.

Of course, just because Gaster didn’t burden Sans with his worries didn’t mean Sans didn’t have plenty of his own.

Even if Gaster couldn’t figure out what they were.

He kept glancing at Sans as he went about the house, putting away his notes from the day, responding to a few emails, and picking up the kitchen that had been left a bit of a mess from this morning—for once, Papyrus had been too busy making sure he had everything ready for his sleepover to clean up the breakfast mess himself, and frankly, it was almost a relief to see him _not_ completing a household duty for once. He was only ten years old. Even if he enjoyed housework, there should be far more to a child’s life than that.

Yes. Even if it was causing Sans some distress, this sleepover was a good thing. It meant Papyrus was making friends. Branching out socially. Finding others to spend time with, rather than just his brother.

Though Gaster suspected that if he asked either one, they would both say that their brother was all they needed.

He stepped out of the kitchen after about ten minutes of picking up, and found Sans in the same spot as he had left him, with just about the same expression. If he hadn’t been able to feel the faint hum of his soul, Gaster would have worried he had fallen down.

He fidgeted in place for another minute, and even though Sans remained perfectly still, Gaster was sure he knew he was there. At last, he cleared his throat.

“So, since it’s just you and me tonight, would you like something special for dinner?”

Sans glanced up at him, but looked away a second later, shrugging. His head tilted toward the arm of the couch, his smile as blank as it ever got. Gaster pressed his mouth into a thin line and wrung his hands, wracking his scattered mind for anything that would help.

“I could make macaroni and cheese. And I promise not to tell Papyrus if you cover yours in ketchup,” he added, trying to smile. That was silly. Sans hadn’t seemed interested in food before. But it was all Gaster had. He took a step forward, one hand reaching out as if to rest on Sans’s shoulder. “Or we could look through the recipe book. I’m sure we could find something that—”

“The other kids called Papyrus dumb.”

Gaster froze, his mouth still open, his bad eye as wide as it ever got. Then his mouth clamped shut, his teeth clacking together.

“What?” he asked, his voice somewhere between desperate and furious, an unfamiliar sound even to him. “Who?”

Sans stared at the wall, his brow furrowed as he pressed his chin further into the armrest. “I don’t know their names. Papyrus won’t tell me. Doesn’t want them to get in trouble.”

Gaster’s chest clenched.

“Were they the same kids who …?”

But Sans was already shaking his head, his eyes still locked on the floor.

“No. He made sure to tell me that. I was gonna make sure he didn’t go if it was them,” he replied. He paused, as if thinking back to it. “Pretty sure he wasn’t lying.”

Gaster’s shoulders slumped. Papyrus rarely lied, and on the occasion he did—usually for someone else’s benefit—he wasn’t very good at it. He had never learned. He had never had reason to learn. Gaster had always tried to make sure his boys felt safe telling him the truth, even if it was admitting a major mistake. He would always be there to listen, to accept them, to help them fix it.

That didn’t mean that life didn’t occasionally give them other reasons to want to hide the truth. He was beginning to suspect that Sans was conveniently “forgetting” to mention things that had happened at school—things that, as it turned out, were almost always incidents of teachers talking down to him, other kids ignoring or teasing him for his intelligence, or the school itself either assuming he was incapable of advanced work or expecting him to do ridiculous amounts of it faster than was possible for anything but a supercomputer. When Gaster had confronted him about it, he insisted it didn’t matter. It didn’t bother him. He could do work on his own level, and he had friends, even if they were more study buddies than people he really hung out with. He was happy enough, or so he claimed. Certainly happier than he had been before he skipped ahead.

And Papyrus …

He knew very well that even if Gaster wouldn’t get mad at them for making a mistake, even if he would handle mistakes made by them or any other children with sensitive communication and problem-solving, that not all adults would.

And Papyrus hated seeing people get into trouble.

Gaster could certainly ask him about it, once he got home from the sleepover. Maybe he could do something. But he doubted it. If he knew Papyrus—and as neglectful as he had been, he _did_ know Papyrus—he would skirt around the truth until he changed the subject entirely, and Gaster would be left just as clueless as he had been before.

Not for the first time, he wondered where he had failed so much as a parent that his sons felt they had to deal with difficult things alone.

Still frowning, Gaster turned to Sans again. Sans still refused to look at him, staring at the floor with a slight crease in his browbone. But it wasn’t the expression Gaster was expecting. He was clearly bothered for his brother’s sake, but it wasn’t the kind of bothered he should have been. Not the same kind Gaster felt. Gaster was shocked. Clueless, guilty, and shocked. But as pained, as irritated as Sans looked …

He didn’t look surprised.

Upset, yes. Angry, worried, certainly. But he didn’t look surprised.

Gaster frowned harder.

“Has this happened before, Sans?” he asked, even though, looking at him now, the answer was obvious. Sans didn’t reply. Gaster’s browbone furrowed. “Sans?”

“Everyone thinks he’s dumb,” Sans muttered, staring at the ground, his eyelights almost completely dark, such a contrast that Gaster could hardly recognize him as his son. He looked to Gaster, almost accusing, pinning Gaster in place with only his stare. “He’s not dumb. You know that, right?”

Gaster didn’t move for a few seconds, struck completely silent by the blatant suspicion in his son’s sockets. Then he clamped his mouth shut, his face softening, in sadness and affection.

“Of course I know he’s not dumb, Sans,” he replied. He almost stepped closer, but Sans was still watching him with those hard eyes, so he stayed where he was. “Just because you have different … intellectual talents than he does, that doesn’t mean—”

“You _do_ think he’s dumb, ” Sans cut him off, his browbone lowered.

Gaster stared. “When did I say that?”

“You didn’t need to say it.” Sans jerked his head eyes, pulled his knees up to his chest, and stared off at the wall, so small where he sat, curled up into a ball, that he looked like he could disappear into the cushions. He looked like he wanted to. “You don’t talk about him as much. When people ask about your kids, you talk about him a little, but then it’s all about me. It’s _always_ all about me.”

Gaster opened his mouth, but the words that should have come pouring out of his mouth just … stopped. He stood there, eyes wide, mouth open, waiting for the words to come. They didn’t.

“I …”

Sans glanced at him out of the corner of his eye. Something like betrayal flashed in his eyes, and he curled up tighter. “You do.”

Gaster’s mouth clamped shut. It wasn’t true. He wanted to tell Sans it wasn’t true, because it _wasn’t,_ he loved both of his boys, he couldn’t have just …

Sans huffed.

“You’re always so … proud of me,” he murmured, as if he didn’t understand it. He turned enough to meet Gaster’s eyes, his browbone furrowed. “Aren’t you proud of him?”

Again, Gaster opened his mouth, but this time, even though he knew exactly what he wanted to say, it still took him a few seconds to get the words to form in his throat.

“Of course I am.”

Sans didn’t react. He couldn’t really frown, not with his mouth, but he could do just as well with only his eyes. He pulled his knees a little closer to his torso and lowered his gaze to his feet.

“He’s smart, too, you know,” he muttered, even quieter than before. “Maybe he doesn’t do physics and math like I do, but he’s smart. He’s got a whole different way of thinking that _no one else_ has and just because you don’t understand it, that doesn’t mean it’s not smart.”

“I know, Sans,” Gaster replied, without missing a beat.

Sans tilted his head to look at him for a second, scanning him, reading him, before looking away again. “No, you don’t.”

“Sans—”

“You think physics and math _matter,_ cause they make sense to you,” Sans cut him off, squeezing his legs so tight against his chest that it must have hurt. “But … just because something isn’t important to you doesn’t mean it’s not _important_. It doesn’t mean _he’s_ not important. He’s special, he thinks different than everyone else, and one day, he’s gonna do something great with it and you’re gonna feel bad you didn’t notice it before.”

Gaster opened his mouth and tried to speak, but again, the words wouldn’t come out. Every argument he would have made, every argument he _should_ have made, disappeared before it could pass his teeth. Sans didn’t spare him another glance, and Gaster did nothing to earn it.

They ate dinner together, but after the dishes were clean, Sans went up to his room, and Gaster spent the rest of the evening in his home office. For the first twenty minutes, he just sat there, running over his son’s words again and again, feeling his chest twist and ache further every time. Then, with a huff, he picked up a pile of papers from work and drowned himself in the mundane bits of research documentation he had been putting off until he finally wandered off to bed.

Gaster didn’t have much time to think about what Sans had told him after that. He didn’t have much time at all lately, what with his work on the Core, and it seemed far easier to immerse himself in a challenging project than to look at his sons and mull over every interaction he had had with him.

He tried to tell himself that Sans had just been reacting to what the children in school had said. That he was projecting his anger at those children onto Gaster.

Because Gaster loved both his sons. He _valued_ both his sons. They were special, in their own ways. And just because Sans was … more skilled in certain areas, and Gaster encouraged that, didn’t mean that he was neglecting Papyrus.

That string of thought must have gone through his head fifty times in two days, and it never got easier for him to believe it.

But he was busy, and he didn’t have time to think about it any more than that.

The weeks went by. Sans’s irritation seemed to disappear, and Papyrus went about his days as he always had. They spent a bit more time together than they usually did, Sans even setting aside his homework in favor of spending time with his brother. His grades were high enough that he could have easily survived them dropping—which they didn’t. Even after skipping several years, he was still breezing through most of the material, and as much as Gaster had hoped Sans would finally find a comfortable challenge in high school, at least the ease of the work allowed him a break.

The whole issue had almost slipped from Gaster’s mind before it finally came up again.

It was nearing the end of the school year, and for as long as Gaster could remember, the school always held a reception before the final week of classes—Wednesday for the elementary school, Thursday for middle, Friday for high. Gaster had never missed it, and with as little time as he had been spending with the boys lately, he made sure that his schedule would allow it, even if he would be busy all of the day before and probably be working afterward late into the night.

It was … awkward, to say the least, being around the other parents, but if his boys could make new friends in their classes every year, then Gaster could certainly talk to a few adults.

Even if he rarely did much “talking,” in at least one sense of the word.

Most monsters understood sign language, and he had tried his best to use it more to get himself used to communicating using his hands. But apparently he had already gained a reputation for being a particularly quiet monster. It was irritating, in some ways, being old and well-known enough that his reputation preceded him, but mostly it was a relief. People greeted him, but they knew not to be offended if he only gave brief responses and rarely held long conversations. He had done that before Sans had skipped all those grades, and he found in the first five minutes after he arrived at the reception that it had only worsened since.

Papyrus’s reception was easy enough, but Sans’s presented more of a challenge. He was still learning the names of Sans’s new classmates, not to mention their parents, even almost a full year after Sans had been moved ahead. He still felt out of place. Just about everyone else here had had years to get to know each other, the kids had been in the same playgroups and their parents had become close friends because of it. Even children who were homeschooled usually went to the same social events as other children around their age, and aside from not being in the same classes, their experience was hardly different from their peers’.

But Sans …

Gaster had never heard of a child who had moved ahead so many grades, and so fast. Usually it was just one year at a time, trying out one year only to find out that it wasn’t a good fit and moving up another. It wasn’t such a huge jolt then. Sans had skipped nearly six years at once—though he was doing remedial work in some of the subjects he wasn’t so innately talented in—and aside from a few parents who had children of Sans’s chronological age and others of his academic age, they were among strangers.

But while Sans likely would have been content to stay in the background, doing his far-more-interesting work, news of a ten-year-old in high school—only nine when he had started, and still nearly top of his class, to boot—wasn’t going to stay secret for long.

And while there were a few murmurs of uncertainty, and one or two of disapproval, to almost all the others, Sans had become a celebrity.

Gaster and Sans separated when they first arrived at the reception. Sans went to the snack table—his favorite place to go when he wasn’t sure who to talk to—and Gaster did his best to mingle with some of the adults. Despite the social discomfort, it was nice to be around people other than the five that usually consumed all of his time. Even if it was just small talk. Even if his mind constantly drifted to the work he could be getting done if he didn’t have to put up with social pleasantries. Even if he occasionally found himself just a little overwhelmed by all the noise and the crowds and wanted to head home.

Sans wasn’t overly fond of crowds either, but if he could do this, so could Gaster.

And he wasn’t about to leave his son alone either way.

For about half an hour, they both mingled, but as usual, they found themselves drifting closer to each other—particularly as some of other parents approached Sans to get an update on his life. Two in particular, a woman named Ms. Patrick—Dimitra, wasn’t that her first name?—and a Mr. Lemming—Gaster was fairly sure he was Dr. Lemming’s cousin—stayed longer than the others, and as Gaster’s latest “adult conversation” trailed off, he stepped a little closer, letting the rest of the idle chatter of the room fade into the background as he focused on the voices nearby.

“So I heard you’re already moving on to advanced calculus,” Ms. Patrick went on, her eyes gleaming with pride.

“Huh?” Sans asked, his attention snapping back up to her. “Oh, yeah.”

She smiled wider, shaking her head. “Every time I see you, I swear you get smarter. It’s astounding.”

“Gaster, you’ve really got to share your secret!” Mr. Lemming added, turning toward him and motioning for him to join the conversation.

But while Gaster straightened with pride, Sans’s shoulders fell. His gaze dropped to the ground before flicking back up.

“My brother’s really good at puzzles.”

“Oh?” Ms. Patrick asked, her smile changing to something Gaster would almost call humoring.

“He makes them all the time,” Sans replied, a little more forcefully, not holding back even a hint of the pride in his voice. “Really good ones. He can make a puzzle out of _anything._ ”

Ms. Patrick chuckled, but it was the sort of quiet, patronizing chuckle Gaster had gotten used to hearing when he started spending time around other parents. The sort of chuckle the other parents would make when their child told them that they were going to make a feast entirely out of mud.

_Oh, isn’t that cute._

“That’s great,” she replied, as if she had said the same thing dozens of times before. “Oh, I’ve been meaning to ask you, do you do tutoring? My son is having a little trouble in math and I think it would be great if you could work with him. We’ll pay you, of course.”

Sans couldn’t technically frown, and sometimes Gaster wondered if that was why it was so difficult for other monsters to see when he was uncomfortable. As long as he wasn’t shouting at them or outright sobbing, it was easy for them to pretend that his smile was real. He looked away, fidgeting.

“I’ve … I’ve never really tutored anyone before.”

“Oh, sure you have!” Mr. Lemming jumped back in, laughing and waving Sans off, as if the idea were ridiculous. “My youngest still remembers how much you helped the class with the science lesson back in second grade when your teacher was out. You could have taken over for the year and no one would have known the difference!”

“Besides, haven’t you helped your brother with his math homework?” Ms. Patrick added.

Sans twitched, like a suppressed flinch. He stared at the ground.

“Sometimes,” he muttered. But a second later, his head snapped up, his eyes flicking between the two adults in sharp defensiveness. “But that doesn’t mean he’s bad at it. He likes other stuff more.”

Ms. Patrick chuckled again, still patronizing, but a bit more sympathetic. She patted his shoulder. “Of course, sweetie. You’re really interested in academic topics, and Papyrus is … well, he’s got to be the sweetest boy I’ve ever met.”

And she meant it. Ms. Patrick had only met Papyrus a few times, but she adored him, as did all of the other parents. Every time they saw him, they always took a moment to pat him on the head and ask him how he was doing, accept his eagerly-offered hugs, and sometimes even bring him candy or toys.

But they always returned to Sans not a minute later.

As if they were trying to assuage their own guilt and pretend that they weren’t ignoring Papyrus to get to his other son.

His _more interesting_ son.

“No,” Sans said, and his voice had hardened, his eyes sharp, his smile as tight as Gaster had seen it in a long time. “It’s not just that. He’s nice, but that’s not _all_ he is.”

Ms. Patrick and Mr. Lemming flinched. They exchanged a brief, worried glance, before Ms. Patrick looked back to him, placing a careful hand on his shoulder and giving him a soft smile.

“I didn’t mean to upset you, Sans. How about we talk about something else, hm? How are you liking your classes? How’s the work?”

“Don’t change the subject,” Sans snapped. All three adults flinched, but none of them could take their eyes off of him. His hands had curled into fists at his sides, his smile curled back into something like a snarl, his eyelights so small now they almost disappeared. His arms trembled even as he held himself firm. “My brother’s smart. Just because you can’t see how he’s smart doesn’t mean he’s not smart.”

Mr. Lemming looked away and cleared his throat. Ms. Patrick fidgeted under Sans’s hard gaze. Finally, she broke it and turned to Gaster, flashing him a brief, almost pleading smile and letting out a chuckle she definitely didn’t mean.

“Gaster, I must not be expressing myself very well tonight. Can you explain to Sans what I mean?”

Gaster stiffened. He spoke to the other parents, certainly. He might not be especially verbose, but he _did_ speak to them—or, rather, sign to them. And usually it didn’t require that much effort.

But as soon as the words left Ms. Patrick’s lips, Sans jerked his head to face him, and his eyes locked on him, begging, _pleading,_ for a response. The response he wanted, the response he _needed,_ even if his brother would never hear it.

He pleaded, even though Gaster could tell, from the dimming in his sockets, that he didn’t believe he would get what he wanted.

Something burned in Gaster’s chest, hotter than anything he had felt in a long time. His teeth pressed together as he looked down at his son, _one_ of his sons, one of his sons that he had grown in tubes because of a silly experiment, sons he had pulled out of those tubes and held in his arms and treasured, and it didn’t matter to him then what they could do, what they would be capable of, because they were his _sons,_ and he loved them more than he had thought he would be capable of loving anyone for the rest of his life.

Then he turned back to Ms. Patrick and Mr. Lemming, watching him with calm, expectant eyes.

He could still see the amusement glowing on their faces.

Like they might brush off a childish whim.

Gaster lifted his hands, and even as his mouth opened, he found them signing along with his words.

“Both of my sons are brilliant.”

Ms. Patrick’s expectant smile vanished. There was no frown, no irritation, just … confusion. She glanced at Mr. Lemming, who looked just as uncertain as she did. But Gaster barely allowed them five seconds of reprieve before he took a deep breath and began to speak and sign in perfect tandem, his mind focusing the motions and the words with more ease than he had felt in decades.

“I apologize that my son snapped at you, but … it’s not acceptable to speak of his brother like that,” he went on. “Papyrus is kind. Infinitely kind, very sweet, just as you said. But he is more than that. He’s so much more than that. Just because his talents are not the same as Sans’s do not make them less valid. Just because Sans’s talents are recognized as gift by a limited education system does not make them worth more than Papyrus’s. I would not want Papyrus to be any different than he is right now, just as I would not wish, for a second, to change Sans.”

He could feel Sans’s eyes locked on him, but for once, he did not return to face him. He held Ms. Patrick and Mr. Lemming in his gaze, holding himself up to his full height, not threatening, but absolute, unwavering. Certain.

“And it doesn’t matter whether anyone else can see it. It doesn’t matter whether anyone else can see his talent, his gifts, his potential. Papyrus is just as much my son as Sans, and he is perfect exactly the way he is.”

Gaster swore that the rest of the room had gone silent, even though he was sure no one else had noticed them. All he could see were the two people in front of him, and all he could hear was his own breathing, and Sans’s beside him, and the inhales and exhales of the two adults standing in front of him.

Mr. Lemming fidgeted, but after a few seconds’ pause, Ms. Patrick’s shoulders loosened. Her eyes went soft, and her smile tilted into a slight smile.

“I never doubted it, Dr. Gaster.”

And before any of them could say anything else, she put her hand on Mr. Lemming’s shoulder and led him away, back toward where another group of parents were gathered around the buffet table, laughing over some joke one of the teachers had told.

Gaster stood alone, forcing his breath in and out and his hands to soften at his sides. He must have sounded like an idiot, blathering away in gibberish they couldn’t understand, even if they could read the signs of his hands. But he couldn’t bring himself to care. He couldn’t remember the last time words had come so easily, and he doubted it would happen again soon.

Even if he never did it again, this once had undoubtedly been worth it.

“Do you believe it?”

Gaster jumped and jerked his head to look at Sans, standing to his right. He could have sworn he had already walked away. But he hadn’t heard his footsteps leave, and besides, there was something odd in his expression now, something caught between confusion, hope, and something painfully close to distrust.

Then the exact words his son had said hit him, and Gaster’s browbone furrowed. “What?”

“What you said. Do you actually believe it?” Sans asked again.

Gaster just stood there. Looking at him. He opened his mouth, ready to offer an easy “yes,” but the “yes” wouldn’t come out.

Because his son wasn’t asking what he seemed to be asking.

If Gaster said yes, Sans would tell him to explain. Tell him to say exactly what was so special about Papyrus, what made him so gifted, so unique, and Gaster would stutter out a dozen things about him being kind and gentle and polite and incredible but Sans would still be waiting for him to say more and Gaster would just repeat himself, over and over, until Sans gave up and walked away.

So Gaster just stood there. Looking back at his son. And never in the past ten years had he felt more like a child, and never had Sans looked more like an adult.

After a minute’s silence, Sans let his eyes fall to the floor without so much as a sigh. No anger. No irritation. Just disappointment.

“i’m going to get some punch,” he murmured, turning on his heels and starting across the room. “Let me know when you’re ready to go.”

And as much as Gaster wanted to stop him, wanted to tell him exactly what he wanted to hear, he couldn’t bring his voice to work. All he could do was watch one of his sons leave as the other one filled his head.

He could tell himself, tell _Sans,_ as much as he wanted that he valued Papyrus’s gifts as much as he did Sans’s.

But he would be lying.

Those parents hadn’t just started believing Sans was “more special” out of the blue. Certainly, they had their own opinions, and he was sure many of them valued Sans’s intelligence above many other qualities. But it wouldn’t have gotten this far if he had stopped it. If he had done or said anything to contradict it.

If he had said a word about his other son while everyone ranted on about Sans.

How long had this been going on? For the past year, certainly, but what about before that? Everyone had known Sans was brilliant before that. They had known that since he was in kindergarten, since he was a _toddler._ How long had Gaster been favoring one son and neglecting the other? How long had he focused on Sans just because he could _understand_ him?

How long had Papyrus just stood there and watched them, smiling as much as he ever had, going about his life as if that was how it should be? As if Sans _deserved_ the attention, the praise, and Papyrus did not?

How many times had he been called “dumb” and his dad hadn’t been there to defend him?

It crossed Gaster’s mind, as he stood there, watching Sans across the room, to run home and find Papyrus and scoop him into his arms and tell him exactly how precious, how important, how _special_ he was. He almost did so. Maybe he would still do so, once they left the reception. But would that fix things? Would that make him see what he had apparently been blind to all these years? Would that make him really change how he behaved, changed how he talked every time he spoke to the other parents, would that make him find a way to change all the parents’ minds when they seemed to have made them up long ago? Would that make sure he gave Papyrus the appreciation he deserved?

He wanted to fix this. He _had_ to fix this. But he had no idea where he was supposed to start climbing out of the hole he had dug himself into.

The hole he had dragged his son in, too.

Gaster stood there for the rest of the evening, watching the other parents pass him by, until Sans come back and asked if they could go home. He nodded without a word and walked them back to the house, silent the whole way there.

By the time they arrived, Papyrus had already gone to bed, and as many times as Gaster tried the next morning to bring it up, the words never came.

He swore he could see Sans’s accusing eyes burning into him the rest of the day.

**Notes for the Chapter:**

> Just a quick note that I hope was made clear in this chapter: yes, Gaster has always subconsciously “played favorites” with Sans and Papyrus. He does not do it out of malice, but out of the fact that he understands Sans’s interests and therefore knows how to place value on them. Papyrus is much less like him in that way, and Gaster doesn’t really know what to make of him, because he doesn’t know what to make of people who are different from him. This is NOT OKAY. Gaster had issues long before he started the experiments on the boys, and this is one of them.


	38. Chapter 31

**Notes for the Chapter:**

> One last time: have you read the tags?

Sans was late.

Of course, Sans was late a lot nowadays. Papyrus wasn’t sure if he even had a “normal” time for coming home that he could be late _for._ It didn’t matter, anyway. Papyrus had waited up for him until three in the morning back when he did those late-night study groups in college, and if he had to wait for him all night now, he would.

Back then, he had waited on the couch, curled up by one of the arms, staring at the door. Now he sat just inside his room, the door cracked open so that he could see the front door just clearly enough to make out anyone who came in. It was a little silly to hide from Sans like this. But Sans looked so sad nowadays, and Papyrus wasn’t sure if he could bear to see him like that.

Was he making him like that? By not talking to him?

Or was he sad about what he was doing?

What he had done.

What their dad was doing.

What he had _let_ their dad do.

Papyrus didn’t get angry very often, and he didn’t even know whether he was angry now. He … hurt. So badly. All of him hurt, worst than the worst of the experiments, and he would have taken a _thousand_ more of those experiments if he could get the little human back.

He tried not to think about what was happening to her, but there wasn’t anything else to do, sitting home alone all day. He didn’t feel like cleaning. He barely felt like eating. For the first time in his life, he just … didn’t want to do anything. All he wanted to do was sit in his room all day and listen for Sans to come home and hope that one evening, he would bring the human back with him, even though he knew it wasn’t going to happen.

But still, he found himself poking his head close to the door when he heard the sound of the front door opening and closing downstairs. As he caught sight of Sans, his soul somehow rose and sunk at the same time, because Sans was alone, but he was home. He was … safe. Sort of. He was safe for now, wasn’t he? At least until tomorrow.

He stopped just in front of the door, turning his head from side to side, like he was … looking for something. Someone.

For Papyrus.

He did that sometimes. Like he would forget that Papyrus wasn’t there. Like he still expected him to be downstairs, maybe in the kitchen, making dinner, or rushing to hug him or ask him how his day had been.

Papyrus’s chest hurt as Sans’s face twisted, then fell into the same blank expression he had worn before. He hated it. He hated all of this. He didn’t want to do this, he wanted to be with his brother, he wished all of this had never happened, he just wanted it all to _stop._ He didn’t want to fight. He didn’t want to be mad or not-mad or whatever he was right now and he wanted his dad back and he didn’t want Sans to be sad.

He wanted to go to him.

He wanted to go downstairs and pull him into a hug and he wanted to go the lab and grab the little human and run.

But he couldn’t make himself move.

And he wasn’t sure if he could bear it if Sans refused.

So he did nothing. He sat just inside his room, peering out through the cracked door as Sans trudged up the stairs, paused for a few seconds in the hall, then slipped into his own room, pulling the door shut behind him.

The walls between them had always been fairly thick, but not thick enough to drown out all noise. Papyrus could just make out the faint sound of his brother’s bare feet shuffling against the floor. He didn’t even seem to bother changing into his pajamas—Papyrus wasn’t sure if he had changed clothes at all in the past few days. The mattress creaked as he flopped down on the bed, and after a minute of settling down, Sans went quiet.

Papyrus waited. Sans had fallen asleep very quickly lately. He seemed so tired now, all the time, and his HP … Papyrus had never seen _anyone_ with HP so low. Once, Papyrus might have been happy that his brother was resting, but sleeping as much as he was now …

… that wasn’t any healthier than sleeping only a few hours a night, was it?

After twenty minutes, he still heard nothing from Sans’s room. He snuck down the hall and pressed the side of his skull against the door, but all he heard was the faint sound of breathing. Papyrus stayed there for a few minutes longer, just listening to his brother, alive on the other side of the door. Then he slipped down the hall as quietly as he could, tip-toeing down the stairs. He opened the door just slowly enough so the hinges wouldn’t creak, and glanced up the stairs one more time before stepping outside and shutting the door behind him.

He started to walk.

It was the same walk he had made every day for a very long time. The walk he made as a kid, when he wanted to visit his dad at work. The walk he had made during Sans’s internship when he had forgotten his lunch.

The walk he had made to meet his dad at the lab, at just the right time so that no one would question him coming in.

It was dark now, but he was used to that. He had come home so many times in the dark. There was no one out to greet him, no one he had to lie to, no one he had to smile for. He just walked, faster than he normally would have, faster than his tired legs wanted to move. Maybe it wouldn’t make much difference if he was there sooner or later. He didn’t even know if he’d be able to get in. But it felt wrong to take any longer than he had to.

Sans wasn’t going to do anything. He knew that, even if he didn’t want to believe it. Sans was going to let their dad go on doing what he was doing to the human. It wasn’t going to end.

But just because his brother couldn’t act, that didn’t mean Papyrus couldn’t either.

The lab loomed over him, like it might swallow him up, but he just held himself taller and stared it down. He pulled out the key card he always kept in his pocket and slid it through the scanner. The door opened. He didn’t think his dad would have changed the code, but it made his bones feel a little less tense once he was inside.

The lights were still on, and Papyrus tried to focus on the bright, familiar space rather than thinking about what was downstairs. _Who_ was downstairs. He stepped into the elevator and pressed the button, watching the doors slide shut in front of him.

Would his dad still be here? He hadn’t come home, and Papyrus hadn’t seen him on the way here. So he was probably still here. Just like he had been almost all the time ever since they took the human away.

Papyrus gripped his arms and hugged them close to his body. His dad would still be here. If his dad was here, he probably wouldn’t even let him in. He would send him home, or maybe he would be mad and want him to stay so he didn’t get into trouble.

Maybe he was still doing bad things to the human.

Maybe … could Papyrus do something to stop him?

He had tried to stop him before, and it hadn’t worked. But … he could always try again. Maybe it would work this time. Maybe he could convince him that the human wasn’t dangerous, she wasn’t bad, she was his friend and he should just let Papyrus take her home and heal her and take care of her.

He would take good care of her.

He had helped take care of Sans when he couldn’t take care of himself. He could take care of this little human, too.

Maybe she didn’t have to leave. Maybe she would be safer if she didn’t leave.

Maybe …

The doors opened, and Papyrus stepped out, his hands trembling and his head held high.

It was darker in the underground lab. Some of the lights were on, just enough for him to see, but most of them had apparently been turned off when the other scientists left for the day. Each of his steps seemed to echo around the halls, no matter how quietly he moved. He listened for anyone nearby, any voices, any movement, but there was nothing. Just him.

His dad was still here, right?

He moved a little faster, following the path down the halls he could have walked blindfolded. When he reached the first private lab, he paused, hovering his hand over the door handle for almost a minute before he finally pushed it open.

The bright light inside made him blink, and for a second, he froze, expecting to see his dad whipping around to face him. But as his eyes adjusted, he found the room empty. No one spoke. No one moved. It was just him and all those machines. The machines he had attached to Papyrus. The machines that had measured things and made him hurt, a little table with scalpels and needles, and a bigger table near the middle of the room with—

There.

There she was, lying on the table. The same table where he had laid down so many times, the same table where—

He moved forward. It was easier not to think about it when he was moving, and he didn’t want to think about that right now.

He moved across the room, tip-toeing even though he knew his dad wasn’t in the room, maybe wasn’t even in the whole building. He had to keep glancing down at his feet to keep from tripping over wires or papers or, in one case, some old food that had fallen on the floor, but the rest of the time he stared at the human, resting on the table.

She was breathing. That was a good thing. Humans needed to breathe. But he didn’t think they were supposed to be that pale. At least, _this_ one hadn’t been so pale the last time he had seen her. She had had little dots on her cheeks—she said they were called “freckles”—but the rest of her had been a pinkish color. Now she looked … almost as white as him. And there were dark circles under her eyes, and her lips were dull and purple. The only part of her that hadn’t changed color was her hair.

He stopped just in front of her. Her eyes were open, just a little, but she didn’t seem to be looking at him. She didn’t seem to be looking at anything. She faced the ceiling, but her eyes were … far-off. They looked like marbles in her head.

He stood there for a minute, shifting his weight from side to side, mouth pressed into a thin line. At last, he cleared his throat.

“hello.”

It was barely a whisper. It didn’t feel right to talk loudly when she was so still.

She didn’t move. She didn’t even blink.

“I … you remember me, right?” he asked with a tiny, shaky smile.

Nothing.

“It’s the Great Papyrus,” he tried. Still nothing. His smile fell. “papyrus. You remember papyrus.”

She didn’t react at all. She … humans didn’t still breathe when they died, right? Did they turn to dust when they died? He had heard somewhere that they didn’t. They just stayed there. But their bodies didn’t still breathe when they were gone, did they?

“you … you can hear me, right?” He knew he wouldn’t get a response, and finally, he focused his attention on her, checking her over. His body stiffened, and his sockets grew wide. “You’re … your HP is very low. You look like a gust of wind could blow you over! Do you want me to heal you?”

She moved. Just a tiny bit, just a little shift of her head toward him, he wasn’t even sure if she could _see_ him with those glassy eyes, but she had _moved._ He smiled, even though it made his mouth tremble.

“You’ll feel better if I heal you.”

Still nothing. She didn’t move anymore. She looked at him, and there was something in her eyes he didn’t have a name for. He wanted to get her out of here. He wanted to take her someplace safe and make sure no one ever hurt her again.

He wanted this all to be over.

He didn’t want anyone to hurt anymore.

He just …

He stepped closer, reaching his hands toward her tiny body.

“But … those straps don’t look very comfortable. I’ll undo them first,” he said. As soon as he touched her, she jolted, as hard as the straps would allow, and squirmed, her eyes far wider than they had been before. Papyrus paused, then gave her a small, shaky smile. “don’t worry. i’m … I’m going to get you out of here. You can come with me and I can take you somewhere safe and we … I can take you to the king. I met him a few times, he’s very nice! He looks a little scary, but he’s a big softie! Big and fuzzy and soft, on the inside, too! He’ll help you. We’ll both help you. We’ll … we’ll get you home, and you’ll be safe, and you …”

His sockets burned, and his breath was shaking, and there was something in his throat that kept him from breathing right. He ignored it. His hands trembled, and it took him a few tries, but finally he managed to unhook the first strap, then the second. As the third strap came undone, she began to move, rolling her shoulders, shifting her arms and legs as if she had forgotten what it felt like to move. Her head turned toward the little table next to her with all the supplies, and Papyrus wanted to throw it into some dark place where no one would ever see it again.

Where those tools couldn’t hurt her anymore.

The fourth strap came loose, and Papyrus smile almost felt real.

“There,” he said, with a quiet satisfaction that felt more like relief. The tension in his bones faded, even as the human stared up at him, her eyes flicking to the table so fast he barely noticed it, her muscles tight when she should be calm, she was safe now, nothing would hurt her, everything would be okay. His hands fluttered near her, unsure, but far more hopeful than before. “You’re free, see? You’ll be okay. Now I can heal you and we’ll get you some food and we can take you to the king and—”

He barely saw the human move before he felt the scalpel slam into his throat.

It didn’t hurt. It should hurt. Things like that were supposed to hurt, weren’t they? But he didn’t feel anything. He didn’t feel her pull out the blade. He didn’t feel her stab him again, in the shoulder, then in the chest, at the top of his skull and his neck again. He didn’t feel his HP slip lower and lower with every blow.

But he could hear her sharp breaths, her angry, sobbing, _terrified_ cries every time she threw the scalpel forward again.

He could see her tiny, pale, trembling body.

He could see her wide, blank eyes, like glass balls in her head, too far gone to even form tears.

He could see everything that had once been such an essential part of her shoved to the back of her mind, as the fierce and overwhelming desire to live took over the rest.

And he could hear the clatter of his own bones as he hit the floor.

The scalpel fell to the ground next to him. A whimper slipped past his throat, even as his vision went fuzzy. He tried to move, tried to sit back up, but his arms and legs wouldn’t hold him. He shifted, and the world tilted, back and forth, side to side.

His eyes fell on the door to the lab. Or … it looked like the door. But there was someone in front of it.

Someone inside, with the door falling shut behind them.

Someone … short and white with big eyes and dirty clothes he hadn’t washed in days, you can’t wear your shirt that long without washing it, Sans, it’s unsanitary, you can’t stop caring about your hygiene just because things are a little different now—

Sans.

His brother.

Staring at him.

Staring just above him, to his left, toward the table where the human still sat.

His eyesockets went dark.

He raised his hand.

Papyrus opened his mouth, tried to cry out, no, no, _no,_ no one had to get hurt, it was okay, don’t hurt her, she’s scared, she can do better, she’s just scared, _don’t hurt her_ —

The bones shot through the air and rammed right through the human’s torso.

She choked, her eyes so wide they almost didn’t look real.

Something dark red slipped out of the corner of her open mouth. More of the red stuff, a _lot_ more of the red stuff, dripped around the bones in her chest and her back, it looked like ketchup but thinner, but why would she be leaking ketchup, why would she be leaking, humans weren’t supposed to leak, were they—

She tilted, wobbled, and fell off the other side of the table.

Her body didn’t clatter when it hit the ground.

It made one loud thud.

And then there was nothing.

Papyrus opened his mouth to call out for her, he didn’t even know her name, he had never asked her name, she was so small, he had to protect her, maybe he could still heal her, he could still make her safe, he—

Someone was touching his shoulders, and Papyrus’s head lolled to the right to face the blur in front of him. His brother. That was his brother.

Sans.

Sans had …

The hands on him lit up, and he could just make out the hint of flashing blue in Sans’s left eye. He felt a tinge of magic, warm and soothing, seeping into his bones. It was … familiar. He had felt that before, hadn’t he? When Sans had healed him. Why was Sans healing him? He was alright. He didn’t even feel anything. He would be fine, they needed to get to the human, if Sans could heal him, Sans could heal the human—

But …

Sans pulled his hands back, staring at them. He was shouting something, cursing, shouldn’t use those bad words in front of such a little human, Sans, he stared at his hands like they were supposed to do something, they glowed, but not as much as they had glowed before, shouldn’t be using your energy if you’re tired Sans, he’ll be okay, that’s what you said, wasn’t it, he’s the great Papyrus, he’ll be okay, he’ll …

Something clattered, and Sans flinched, but didn’t turn around.

Papyrus’s eyes shifted, just enough to see the door open again, someone else standing just inside it.

Someone …

He knew them. He knew their name. They were tall and bones, they were made of bones, and they were staring, wide sockets, mouth open, they looked … they looked upset, they looked …

He wanted to go to them.

He wanted to tell them it was okay. Him and Sans, everything will be okay, no matter what, just stay together and everything …

The edges of his vision turned to black, Papyrus’s sockets shut.

His breath shuddered as his body went limp.

And just before his mind faded to nothing, Papyrus felt the bones of his arms and legs crumble into dust.

**Notes for the Chapter:**

> Remember, if you kill me, you don’t get another chapter. 
> 
> I’m so sorry.
> 
> (Also, it's worth mentioning that back in March, when I was still planning this story, I told a good friend of mine that I was thinking of doing something horrible in this story. I didn't tell them what it was, but they told me to do it. I agreed, but on the condition that I immediately point the finger at them when I did it. I'm ... not going to do that, because my cruelty is not their fault. But they know who they are and now they can yell at me THAT IS NOT WHAT I MEANT.)


	39. Chapter 32

**Notes for the Chapter:**

> Will apologizing again put me back in you guys' good graces?

Sans was screaming.

Gaster knew that, but he didn’t hear it. He didn’t hear anything. The Core could have exploded right next to his ear and he wouldn’t have made out the faintest whisper.

But he could see Sans on the ground, his hands pressed to his sockets, his body shaking and jerking.

He could see the pile of white dust sprinkled thickly over Sans’s shirt and pants, the rest of it spread out around him on the pale tile floor.

He saw it. But he couldn’t understand it.

He couldn’t accept it.

He didn’t know how long he had been standing there. He didn’t know how long it had been since he had burst into the room, ready to summon a bone at a second’s notice, ready to reach out and grab the human’s soul and slam it back onto the table even though he didn’t know how it had managed to escape.

And now, all he could do was stand there, useless, and stare.

The alarm had been set up quickly, in under an hour, when the human was recovering from an experiment and he had nothing else to do. He doubted it would escape, but he had to have a backup plan, just in case. Something that would be sure to get his attention if it happened to get free from its bonds.

He hadn’t even recognized the alarm when it first went off, and it had taken a minute before he reacted, spinning around where he stood near the supply closet and racing back toward the lab.

He hadn’t been away long. At least he didn’t think so. But he hadn’t had a clock with him, and his mind had been … funny nowadays. He had never kept track of time particularly well, and now, the only thing that marked the passage of time in his head was coming to or leaving the lab, and the growing pile of notes on his desk.

How long had it been since he had started the experiments on the human?

How long since Sans had found him out?

How long since Papyrus had agreed to take his brother’s place?

How long since Sans had stood in this lab in front of him, telling him that it would be worth it, it would be worth whatever he had to go through to get them out of here?

He hadn’t wanted to do it, had he? He had thought of it, but he hadn’t _wanted_ to do it. He had spent days mulling it over before he even _mentioned_ it to Sans, and after that …

How long ago had that been?

How long had it been since he smiled at Sans? Really smiled at him? How long had it been since he hugged him? How long since he had hugged Papyrus? Since he held him in his arms and felt with every breath how much he loved him?

His son.

His sons.

Papyrus and Sans.

Sans and Papyrus.

The two tiny skeletons that had appeared over the weekend in the jar of nutrient fluid he left on his desk.

His … sons.

The infants he had carried around on his back and chest as he went about his lab work. Who had curled up on either side of him at night to sleep for years, slipping into his bed on occasion long after he had given them their own. Who had fed him little bits of their breakfast when he forgot to make some for himself, who had set on his chest and refused to move because “Daddy, you need to get some sleep, too!” Who had greeted him every day when they came home from school, or when he got back from work, even if it was late. Who had made him breakfast in bed and a handmade card on Father’s Day. Who had never been afraid to bonk their little skulls against his in a goodbye kiss, even in front of the other kids.

His sons, who had offered to be his test subjects because there was _no one else who could do it._ Who had put up with his negligence, who had suffered through his worst moments.

His sons …

Sans and Papyrus.

Sans, who he had stopped experimenting on only to go behind his back. Who he had locked in a closet and forced to listen to his brother’s screams.

Papyrus … who kept saying that he was good. That he loved him. Who never stopped calling him “Dad,” even when Gaster brought him closer to death than he had ever been.

Papyrus, who had cried for him not to hurt the human.

Papyrus, who …

… who was …

Gaster looked at the dust spread out on Sans’s clothes. On the floor.

The dust that had once been bones.

The dust that had once been …

Sans’s screaming had died down, and came out now as a high-pitched keening, as if he couldn’t bring himself to stay quiet. The sound broke every few seconds when his breath hitched in sobs, when some lump in his throat kept the sound from coming through.

He was crying.

He was crying so hard it barely sounded like crying.

Sans … his son was crying.

He should go to him. Why was he just standing there? Why wasn’t he going to him? This was his son, it was his job to take care of him, maybe he didn’t always know what to do, but he had to _try,_ that was what Dr. Japer always told him, as long as you’re _trying,_ you can get better, even if you mess up once you can always get better in the future, you can always make a better choice the next time.

He should go to him.

But his feet wouldn’t move.

And his eyes kept falling on the dust.

Dust.

He had to get to his son.

His son.

But which …? Where was …?

Sans.

Sans didn’t even know he was there.

Sans didn’t even …

Wouldn’t he have gone to him, when he was upset? When he was sad? When he was sad? He had always … even when he was an adult, even when he was so determined to hide, he would still go to him if things got truly bad, he always …

But he had stopped.

He had stopped when …

… he had stopped because Gaster had hurt him.

Hurt him. Then hurt Papyrus.

Gaster had hurt them. He had hurt his sons.

He had experimented on them, long after it passed the limits of being consensual, something they had all _agreed_ on. He had forced them through pain they had never expected, he had pressured them, manipulated them, he had used everything he knew about them to make sure that they wouldn’t stop him, he had locked Sans up, he had threatened to hurt Papyrus, he _had_ hurt Papyrus, and Sans, over and over and over and—

He had tortured them. Tormented them. Traumatized them.

He had made them lie to each other.

He had split their unshakeable bond right down the middle.

He had taken away something precious to Papyrus. And Papyrus had done everything in his power to get it back, to protect it, and it had—

The human had—

Because of Gaster.

Because of everything he had done.

The human hadn’t touched him before. And now it had … when anyone with _any_ sense would know Papyrus would never hurt them …

Because of Gaster, Papyrus—

His mind wouldn’t work. He tried to process the words, but he couldn’t push them through his thick skull. He felt … empty. And alone. He had spent decades cooped up in this lab, centuries, _millennia,_ but he had never felt so alone.

He didn’t want to be alone.

He had been a father almost twenty years now. Twenty years, and it was the first time he had genuinely felt that he didn’t want to be alone. Never again. Or maybe he had felt it for a long time and just hadn’t recognized that this was how it felt.

He didn’t want to be alone.

He thought the words, but they didn’t make sense. He looked at the dust, but his mind refused to accept what it was. He looked at his son, his li—he looked at Sans. And only after another few minutes of standing there, staring at him, did he finally managed to move.

If there was a broom around here, he had never used it. And he didn’t want to use a broom. He didn’t even remember what people _did_ use to do this. It had been far too long since anyone close to him had …

He picked up a mason jar from a nearby counter and knelt without thinking, scraping the dust from the floor and into the jar. It took several minutes, and he kept missing some, and Sans was still sitting there, sobbing so hard he barely made any sound. Gaster tried once to reach over, to get the dust off his clothes, but Sans just cried and jerked back, scrambling up against the closest counter and burying his face into his knees. Gaster didn’t try again. He gathered every spec of dust he could pick up with his bare hands, and only then did he find a lid for the jar and cover it, as tightly and carefully as he could.

He shouldn’t be using a jar. It wasn’t right to use a jar. Monsters had used all kinds of things, of course, it wasn’t like they were _permanent,_ just something to hold the dust until it could be scattered properly.

A jar.

A mason jar.

How many mason jars did he have around here? He rarely used them nowadays, when other methods of containment were available and far more efficient. If he had one now, he must have had it for years.

Had he ever gotten rid of the one the boys had been grown in?

The thought lingered in his head for a minute, freezing him in place, before he pushed it away and slipped the jar into his bag.

He paused for only a moment before he walked around to the other side of the table, to where he had glimpsed the tiny body when he first came in. The human wasn’t moving. He had gotten used to seeing its chest rise and fall, no matter what he had done to it, whether it was awake or asleep. There was no movement there now. Just one long white bone, sticking out through the front and back of its chest. Its eyes wide open, staring out into the distance, while blood trickled out from its parted lips.

Was that what a dead human looked like?

All this years, all those other humans, and he had still never seen what one looked like dead.

But there was no curiosity there. No desire to take notes. Gaster’s eyes shifted upward, just above the chi—the human’s motionless chest.

Toward the glowing yellow heart floating above.

Right. That was what happened after death, wasn’t it? At least … he thought it was. It wasn’t like he had ever been around to see it.

In the back of his mind, he wondered if this should have felt more important. If he should have been … more excited to see another soul, _one more soul,_ one step closer to their freedom.

Their freedom.

They …

He didn’t feel anything. He _couldn’t_ feel anything.

He gripped the soul with blue magic and shoved it into the first storage container he could find, then stuffed it into his bag alongside the mason jar without another thought.

Sans had stopped moving now, his breath still hitching with sobs, tears still dripping down his cheekbones, but no longer wracked with such desperate emotion that he couldn’t keep still. No longer crying out into the silence. He seemed to have frozen in place, and Gaster had no trouble slipping his hands under his arms and lifting him into his hold. It had been years since he had picked up his son, even though he had carried him around far longer than Papyrus, if only due to his size. Sans had never minded being carried, even as a teenager, but for so long that had been Papyrus’s self-assigned job: picking up Sans when he had run himself to exhaustion and carrying him to a safe, comfortable place to sleep.

Papyrus should be carrying him. Papyrus had earned the right to carry him.

But Papyrus wasn’t here.

And Sans didn’t protest.

Gaster wasn’t sure how he managed to get out of the lab without use of his hands. He must have balanced Sans using one arm at some point, or used his elbow to press buttons. He didn’t remember. He didn’t care. Either way, he found himself outside of the lab, walking through Hotland, back toward home.

Funny that he hadn’t thought of it as “home” for so long. It had just been a house where he went when he wasn’t at the lab.

Decades ago, he had joked that the lab _was_ his home, and his house was just a backup living area for if the lab was unavailable.

He had stopped making that joke after his sons were born.

He hadn’t even noticed.

It was only when he pushed the front door open that he realized that it wasn’t locked. Sans always locked it when he came home. Was that a way to try to keep him out? Even though he knew it would fail? Hadn’t he always left it open before, if he came home before Gaster?

Papyrus still left it open, though.

He hadn’t locked it when he left.

He had never liked locking doors when he could avoid it.

The house was still lit. Papyrus hadn’t turned the lights off, apparently. And Sans … he had gone home, Gaster was sure of that. How long had it taken him to notice that Papyrus was gone? He hadn’t thought to lock the door behind him either.

Gaster stood in the living room, and he swore he could hear the phantom of two excited voices calling out for him before they threw themselves in his arms. His grasp on Sans tightened. Sans didn’t notice.

He was still so small. So fragile.

Gaster climbed the stairs on stiff, wobbly legs, slipping through the open door of Sans’s bedroom. It had been weeks since he had been in here. He didn’t think it had ever looked this messy, clothes strewn on the floor, bed unmade, curtains pulled shut when Sans had always liked them open. It didn’t feel like Sans’s room. It didn’t feel like the room that had once belonged to two little skeletons who waited years after leaving his bed before they were comfortable sleeping alone.

Sans didn’t seem to notice when Gaster slid him onto the mattress, as carefully as he had when he was a babybones and fell asleep on the couch, only for Gaster to carry him to bed later on. Tears still streamed down his cheekbones. His breath still hitched. But his eyes were shut, and his body had gone mostly limp.

Gaster had never seen someone cry in their sleep before.

He didn’t want to see it again.

He covered Sans with his blankets, tucking them around him on a reflex he had almost forgotten, before he slipped out of the room and closed the door behind him. Then he stood there, in the hall, his bag dropped to the floor, taking out the jar to hold it in both hands, cradling it as gently as he had cradled the tiny little skeleton he pulled out of a tube.

His feet moved before he could think to move them himself. He found himself wandering up and down the hall, not sure where he was going, or why. His eyes shifted from side to side, his arms curled around the jar, hugging it to his chest, just like he might have hugged a small child.

Everywhere he looked, there were pictures on the wall. Of course there were, he had put them there himself, spent hours finding frames and picking out the perfect places to hang them. He hadn’t noticed them in a while, they had been there so long, but he had put them there, hadn’t he? At least at first. He had added more and more over the years as they got more pictures, until Sans told him that just because a photo was adorable, that didn’t mean he had to hang up _every single one._

Maybe that was why Papyrus had taken up making scrapbooks. Maybe he wanted to find another way to display all the special moments of their lives without making their walls so full that they forgot what color the wallpaper was.

He had always been the one to hold onto every precious experience their family shared. Even when Gaster was too busy. Even when Sans buried himself in his studies and his internship, even when Papyrus spent countless hours by himself, even when Sans got the job he had always wanted and Papyrus knew that his brother and his dad would be spending all their time together and he would just be home alone, he had never complained, he had just supported them, always supported them, always there, no matter how bad things got.

He had come to support Gaster.

Made him his favorite dinner and brought it to his lab.

Offered to listen. Offered to help.

And Gaster had …

Gaster had …

His knees buckled, and a second later he was on the floor, gasping, he couldn’t breathe, he didn’t need to breathe but he _had_ to breathe and he couldn’t breathe and …

No. No no no no _no._

It wasn’t …

None of this was …

It was a bad dream. But it wasn’t a dream, he knew what dreams felt like, he had had dozens of them when the boys were first born, dreams where he failed them, dreams where they died because he was too careless, dreams where he realized exactly why he should have given them up from the very first day, he wasn’t cut out for this, he would never be cut out for this, he wasn’t supposed to be a father, he had never _wanted_ to be a father, and he … he …

He looked down at the jar in his arms, and for the first time, he really looked at it.

That dust.

That dust had been …

His son. He had experimented on his _son_. Both of them, he had tried one and when he left he dragged the other in, lied to him, manipulated him, taken away his smile, taken away his hope, taken away everything he held dear until even he couldn’t keep up a smile.

He had stolen everything.

And still Papyrus had tried to get it back.

One more try.

Just one more try.

And now he …

Gaster choked on the sob forcing its way up his throat, swallowed one back just as another rose to take his place, and suddenly it didn’t matter that he couldn’t breathe, he didn’t want to breathe, he didn’t want to be here, he didn’t want to be _alive,_ he wanted it to be over he wanted to wake up he couldn’t take this it wasn’t real it couldn’t be happening but it was and it was his fault his fault _his fault._

Papyrus was dead.

His son was dead.

His son was …

No. No, he wasn’t, he could _not_ be dead. He couldn’t lose him. He couldn’t lose his … he couldn’t lose him. No. Not like this, not so soon, he was _nineteen,_ he had so many years to live, so much to see, he had to see the Surface, he had to see the _sun …_

Everything he had sacrificed, everything he had suffered through, _everything Gaster had ripped away from him …_

It couldn’t be for nothing. He couldn’t just … Gaster wouldn’t _let_ him …

He would live. He _had_ to live. One way or another …

Gaster’s hands tightened so hard around the jar in his hands that it nearly cracked, his other hand slipping into the back at his side to touch the container that barely fit within the fabric.

He pushed himself to his feet, taking just a moment to feel the faint thrum of Sans’s soul from inside the bedroom to his right. The ache, the empty, pained loss, echoing back through his own soul.

Then he ran down the stairs and through the front door, into the night outside.

**Notes for the Chapter:**

> A quick clarification: does Gaster love his sons? Yes. He loves them very much. Even when he was torturing them, he still loved them.
> 
> But feelings do not excuse actions. Many, _many_ parents have done very harmful things to children "for their own good" (thankfully most parents don't torture their children, but the same principle applies). Most overtly abusive parents still claim they love their children. Go back a hundred years, and you'd find the majority of Western parents beating their children to the point of visible injury (considered child abuse today, and rightly so) - these parents still loved their kids, but they were doing what they believed was right.
> 
>  _Feelings do not excuse actions_ , and it doesn't matter how Gaster feels about his sons, or whether he believed his actions were right: he tortured them and led to one of their deaths. This is entirely his fault.


	40. Chapter 33

**Notes for the Chapter:**

> Fair warning: what happens in this chapter will probably make you angry. At the characters, definitely, and probably at me, too. There's a chance it might make you want to stop reading. But I humbly ask that, if you have enjoyed the story so far ... keep reading a little while longer. See what happens. And if it doesn't turn out how you want, then by all means, kick this story to the curb.
> 
> Enjoy. ;)

It took Sans a long, long time before he realized he had woken up.

It was funny. Normally he could only lay in bed for a minute before his eyes opened and everything crashed down on him. But today … this morning—if it was really morning—he just laid there, his mind in a haze, everything faraway, so distant it didn’t matter.

He didn’t want to leave.

He wanted to stay there. Just lay there, forever, not thinking about anything.

Where nothing hurt.

But he couldn’t lay there forever. He didn’t know how long it took for his eyes to open, for the first glimmers of light to reach him. But finally, they did, and he blinked heavy sockets open to stare at the window on the other side of the room.

Something … something had happened.

Of course something had happened. Something always happened nowadays. But … there was something more than usual. Something he was forgetting. Something … important. He lay there, staring at the light and trying to remember how he had gotten to bed. His memories had been blurry before. Plenty of times. More and more as the days went on. After all, if he was forgetting what changes he made to the machine …

The machine.

The machine he was building to …

To get his dad back.

To get … Gaster back.

Because Papyrus …

… Papyrus …

Papyrus was …

Sans couldn’t breathe. He couldn’t think, he couldn’t move, all he could do there was lay there and stare at the wall and no, no, no, _no,_ he wasn’t … he couldn’t … it was a dream, it was just a dream, he couldn’t … but he had seen the dust, he had _felt_ his brother crumble away in his arms and …

“SANS!”

Sans jolted.

And before he could even turn his head, his door swung open, and a figure stood there, tall, almost tall enough to bump his head against the top of the doorway, arms crossed over his chest and a hard frown set on his face.

“YOU LAZYBONES, IT’S ALMOST TEN! I WON’T HAVE YOU SLEEPING THE DAY AWAY, TODAY OF ALL DAYS!”

Sans sat up so fast he almost fell off the bed. The covers slipped off of him as he turned to face the door in full, it wasn’t real, he was hallucinating, he was still dreaming, but—

His brother.

His brother was standing in the doorway.

Intact.

Alive.

Frowning at him.

“I KNOW IT’S BEEN A DIFFICULT DAY,” he said, his face softening, just a bit. “OR APPARENTLY IT HAS. SO JUST THIS ONCE, I WILL HELP YOU GET READY. WHERE ARE YOUR CLOTHES? UGH! WHY ARE ALL YOUR CLOTHES ON THE FLOOR? IT’S A MESS IN HERE! HOW CAN YOU EVEN TELL WHAT’S CLEAN AND WHAT’S DIRTY? I’M GOING TO HAVE TO WASH EVERYTHING AND IT WILL BE SUCH A WASTE AND—”

Sans didn’t even feel himself moving.

One second he was sitting on his bed, and the next, his arms were tight around his brother, squeezing so hard it was a wonder he didn’t snap his spine in two.

“SANS? SANS, WHAT ARE YOU DOING?”

Sans couldn’t choke back the sob that bubbled up in his throat. He couldn’t talk, he couldn’t think, the only thing he knew was Papyrus, Papyrus, _Papyrus right there in front of him and he was alive and he wasn’t dust and—_

“SANS! SANS, SAY SOMETHING! SANS, WHAT’S WRONG?”

But Sans barely managed to breathe. Hot tears slid down his cheekbones, soaking his brother’s shirt, and he didn’t _care,_ because he was _here_ and he was _real_ and everything was going to be okay and it had just been a dream, a bad dream, he was okay, they were both okay, everything was going to be fine but _god why did it still hurt so bad._

Not dead. Not dead. Papyrus wasn’t dead and everything was alright.

His brother was still talking, but Sans didn’t listen. All he felt was Papyrus’s arms slipping around him and hugging him, not quite as tight, but firm enough to make some of the tension slide out of Sans’s bones. Sans nestled closer, clinging to his brother’s clothes, pressing his face into his ribs and muffling the sobs that forced their way up his throat. Papyrus stroked his hand up and down Sans’s spine, like he had when they were little, and Sans snuggled closer still.

And for a moment, just a brief moment, everything really was okay.

Then Papyrus’s arms slid away from him, and Sans forced his sockets opened and stepped back to give his brother a grin.

Sans stopped.

Papyrus’s face looked … healthy. Smooth and white and smiling, without a care in the world. It was, quite possibly, the most welcome sight Sans had seen in his entire life.

And it was wrong.

It had been weeks since Papyrus had looked like himself. Weeks, though it had felt more like months. And even though Papyrus had been spared the physical experiments since Gaster found the human, he had never looked any better. The dark circles remained under his eyes, his bones remained a bit more brittle than usual, and that haunted, fearful, _betrayed_ look had never left his sockets.

This Papyrus … it was like someone had plucked him out of the past. Untouched. Unmarred.

And …

… what was he wearing?

Papyrus had a lot of outfits. More outfits than Sans could count, ranging from the fairly usual shirt and pants to outfits that would be better suited for a costume party. But no matter how eccentric, he wore every one at least once per month, strutting about with the same amount of pride, as if unwilling to choose a favorite.

And while he might never have counted them, Sans could recognize every single one.

Papyrus did not own a T-shirt with the word “jogboy” printed on the front.

The rest of the outfit … it was _similar_ to the things he had seen Papyrus wear, but not the same. It was possible that he had gone shopping, or to the dump, but Sans doubted it. Papyrus hadn’t seemed in much of a shopping mood for a while.

But he did now. Now, the only thing that marred his bright and cheery face was a frown of concern and a slight furrow in his browbone.

“WHAT’S WRONG?”

Sans stared for a moment longer, taking it all in, struggling to kickstart his frozen mind. At last, he managed a smile, just a little wider than his permanent grin, just enough to—hopefully—look convincing.

“nothing, bro,” he murmured, his voice sounding almost steady. “just a bad dream.”

“HM.” Papyrus frowned for a moment longer, looking him over. The worry didn’t seem to go away, still gleaming in the back of his sockets, but still, Papyrus took a step back, head held high as if his decision had been made. “WELL, YOU CAN TELL ME ABOUT IT LATER. NOW, YOU NEED TO STOP BOONDOGGLING AND GET OFF TO WORK. UGH, YOUR CLOTHES ARE FILTHY, HAVE YOU BEEN EATING POWDERED SUGAR IN YOUR BED AGAIN? OH, NEVERMIND, I WILL JUST HAVE TO WASH THEM WHEN YOU GET HOME! YOU’RE ALREADY LATE AND YOU’VE GOT A MUCH LONGER WALK TODAY!”

It took Sans a minute to realize how odd that sounded, just as long as it took him to notice the white powder Papyrus was trying to brush off of his shirt. But by then they were already downstairs, and Papyrus was shoving several protein bars into his hands, mumbling something about not being able to find any decent food in this weird kitchen. Sans took them and stuffed them into his pockets, and Papyrus didn’t protest when he muttered that he would eat them once he got to work. Less than a minute after that, he was out the door, glancing over his shoulder only once, long enough to see Papyrus standing in the doorway, waving at him, his mouth stretched into a smile so familiar, yet so foreign, that it made his soul ache.

This was a dream.

This was a really, really weird dream.

Or … maybe last night had been a dream.

Maybe the past few weeks had been a dream.

Maybe … maybe the past few months had been a dream.

It sounded silly, ridiculous, way too hopeful, but … it was possible. He had had bad dreams before. This one blew all the others out of the park, but … it was still possible. Maybe only the first experiment had happened. Maybe it hadn’t happened at all. Maybe he was still sitting in that chair with the machine pointed at his eye, waiting for the pain to come, or maybe it had already come and he was unconscious and this was the hallucination his head put together to keep him from going insane.

Maybe his dad was still his dad. Maybe his brother had never lost his hope, his health, his _life._

Maybe the human had never fallen.

Maybe … maybe everything would be …

He walked faster, faster than he would have thought himself capable of the day before, with his energy as drained as it had been. For the first time in weeks, if not months, he found himself noticing the people he passed. Familiar faces, people he had seen but didn’t know the names of, people he had never seen before. How many times had he walked this path without noticing them? How many times had he ignored them, even if they stopped to say hello?

Would he start greeting them again?

If this was a dream, had he ever stopped?

He didn’t pause to greet them now. He couldn’t. He had to be sure. He had to …

It took him three tries to get his key card out of his work bag before he managed it, and another five to swipe it right. When the door opened, he stumbled in so fast he almost tripped, all but running across the floor of the lab to the elevator. There, at least he managed to press the right button on the first go, but found himself shifting from foot to foot as he waited for the doors to open again. He actually did trip when he got out of the doors this time, falling face-first to the floor, but he was back on his feet before he could register any pain.

It wasn’t like he hadn’t felt enough pain lately, even if it hadn’t been real.

He ran all the way to the lab doors, but when he reached them, he stopped. He paused. He closed his eyes and took a deep breath, holding it.

Please. _Please._ Stars, if there was any chance, if there was _any way,_ he would do whatever it took, he would make the right choices, he would fix all of this, if he _could_ fix all of this …

He put his hand on the door and pushed.

The hinges barely creaked as the door opened, and the view of the lab spread out before him. It took him less than a second to locate Ga—his dad … was that his dad again …? … standing across the room, in front of a desk. He wasn’t wearing his lab coat. Sans couldn’t remember the last time he had seen him without it. Or … no, he could.

If this was before then … before Sans had shoved the coat back into his hands …

Sans looked down at his own outfit, thought of the coat he hadn’t touched in over a month. Would he start wearing it again? Would he be proud of it, like he had been proud before? Would he look down at his nametag and grin and remember how happy he was to be working here, with the man who had inspired him for so many years?

Maybe it had really been a dream. Just a dream. A long, bad dream. Maybe Papyrus was just trying out a new outfit, maybe he was acting funny for some other reason, maybe there was some explanation for all the weird things this morning, maybe everything would be okay and …

Sans took a step forward, his head higher than it had been in weeks, his eyes wide, his smile just daring to twitch up into his cheeks.

Then Gaster turned around and looked at him.

And Sans didn’t need to say a damn thing.

He could barely recognize the man who used to be his dad nowadays. He couldn’t look at the man who experimented on his own son, who experimented on _Papyrus,_ and believe it was the same man who had read Fluffy Bunny to them twenty-seven times in a row without complaint.

But some things hadn’t changed.

And no matter what else was different, Sans could still look at Gaster and know, without a doubt, that this was the same man who had watched his son turn to dust just the night before.

Sans pushed the door shut behind him and curled his hands into tight, trembling fists.

“what did you do?”

Gaster looked away, calmly, and stared at the papers in front of him, though he didn’t seem to be reading them. Sans sucked in air like he was suffocating, like he _could_ suffocate, as his bones tensed further.

“he … he was … he was _there._ he was _right there_ but he …” He gritted his teeth and took a step forward, his sockets almost completely dark. “what did you _do_? ”

For more than half a minute, Gaster didn’t say anything. He didn’t move. He didn’t speak. He just looked at the papers. Sans grew tenser and tenser, his mind racing so fast it threatened to burn out, and at last, he began to move his foot forward.

“Even when you were young, I knew you were brilliant,” Gaster said, his voice unreadable, his eyes still on the papers. Sans stopped. Gaster didn’t turn to face him. “In so many ways. If you were passionate about something, if you wanted it badly enough, you could do _anything._ You could surpass obstacles that other monsters spent centuries struggling with.”

There was something nostalgic in his voice, something fond, something … proud. And Sans hated it.

“what the hell are you talking about?” he bit out, moving forward again, even though his legs wouldn’t stop shaking. “what did you do to pa—”

“It is incredible, though,” Gaster cut him off, lifting his head, though he still didn’t turn to meet Sans’s eyes. “That you could spend all that time working on that machine and think you had failed, when you had just been succeeding in another way entirely.”

Sans’s mind stuttered as the words began to click.

“my …”

Gaster looked to him at last, something like boredom and a touch of disappointment in his eyes, though it was far outweighed by that fond nostalgia. “You’re far too intelligent to believe I wouldn’t know where you were going every day, Sans. And I know you don’t think so little of me as to think I wouldn’t have a spare key.”

Sans stared a moment longer. Then his head kickstarted again, and he felt his fingers curling, tighter, so tight they hurt, his browbone furrowing and his smile tight.

“so the whole time … you’ve been …”

“Not the whole time. But for the past few weeks, I’ve been keeping an eye on it,” Gaster replied. He turned back to the paper, and this time, he actually seemed to be looking over it, though it didn’t have his full attention. “I knew you were working on something important. And I suspected it could be very useful to all of us in the future, even if you could only think of one purpose for it.”

He turned his head one more time. There was something in his eyes, something Sans couldn’t recognize, something he couldn’t name.

“I was right,” he finished. “Of course, it needed a few … tweaks to make it work properly. But you had already done most of the work for me.”

Sans’s whole body had already begun to shake from everything running through his head, the things he didn’t want to face, the things he couldn’t ignore. His browbone lowered. “funny how quickly that stopped being my ‘private’ lab.”

“Funny how so much of the S.E. we collected disappeared without a trace,” Gaster shot back. Sans straightened. But Gaster didn’t sound angry, or even irritated. He was just stating facts. He looked at Sans for a long moment, with the same scrutinizing gaze he had given him during those later experiments, though not quite as hard. “I wonder how long it would have taken you to realize what your machine was capable of on your own.”

“stop rambling and tell me what you _did_ ,” Sans hissed.

Gaster went silent for another ten seconds, and if the expression on his face hadn’t looked the way it did, Sans would have suspected he did it just to spite him.

“You wanted your machine to take you back in time, correct?” he asked. Sans didn’t respond. Gaster, apparently, wasn’t expecting it. “But as you know, time travel into the past is far more challenging and complicated than almost any scientific endeavor that has ever been taken on.”

Sans took another step closer, eyes burning, accusing, very close to completely black. “you said it worked. you said you _did_ something with it.”

“I did do something with it,” Gaster said, eying Sans with unreadable eyes. “You wanted the machine to travel back and forth along _this_ timeline. And it won’t go back and forth. It stays at exactly the same point in time and space … no matter what timeline it is in.”

Nothing. Sans looked at him, stared at him, ran the words over a hundred times in his head.

“… what?”

Gaster stared at him with the smallest touch of impatience in his eyes. “You were already studying parallel universes, Sans. I’m honestly surprised you didn’t realize that your machine was capable of reaching them.”

“ _reaching_ them?” Sans breathed, struggling to find words to express himself when he couldn’t even understand what he was hearing. “what … you … that machine … it _went_ to a parallel universe? _you_ went to a parallel universe?”

“Of course not,” Gaster replied, as if it should have been obvious.

Sans’s shoulders fell, just a bit, even though his head still swirled and god, he really needed to sit down before he fell over.

“I had to search through far more than one to find what I was looking for.”

Sans didn’t even have the presence of mind to tense back up again.

He just stared. Stared at the man in front of him, talking about something he had only begun to think _might_ be possible a few months earlier, something he wasn’t even sure would be possible in his lifetime, if ever. He had talked about _looking_ into parallel universes, but … _going_ to them? Physically reaching them?

In his machine. The machine he had only just hoped might be able to take him somewhere else in _this_ timeline. And it had reached …

“There were far, far more universes where neither of you ever existed,” Gaster went on, and though his voice hardly changed, there was something in it this time, something … distant, wonder-struck, as his gaze drifted to a point high on the wall, as if he saw something completely different. “But I found one. Very similar to our own. There may be some … adjustments, some things that need to be explained away, but … I expect he’ll never know the difference.”

Sans was so, so close to asking what the hell he was talking about.

Then Gaster looked back.

Sans couldn’t breathe.

His sockets grew, and his soul stuttered, and his bones threatened to collapse under his weight from how hard they shook.

“papyrus … he …”

Gaster put a hand to his face in a gesture that might have looked exasperated if not for the pinch in his browbone, the tight line of his mouth.

“I don’t know exactly what things are different, but he clearly knows you, Sans. That’s the most important part. We just need to—”

“that’s _not_ him!” Sans spat, so loud his voice echoed, so loud Gaster dropped his hand to look at him. Sans’s breath came in trembling huffs, his whole body so tight it hurt. He shook his head, slow at first, then faster and faster until his skull threatened to detach from his neck. “that’s not … that’s just some stranger, that’s not …”

His voice trailed off. His head slowed to a stop, and his eyes fell to the ground in front of him.

He could still see Papyrus looking at him this morning. Standing in his doorway, berating him for sleeping in … Papyrus berated him for plenty of things, but hadn’t he always wanted Sans to get _more_ sleep? He should have noticed then. He should have realized right then and there that it wasn’t _his_ Papyrus, it wasn’t his brother, it wasn’t the _right_ one, it wasn’t …

But …

The way he held Sans while sobbed … the way he rubbed his back, the way he looked at him when he asked what was wrong. The way he hesitated when Sans said it was nothing. The way his bones felt against Sans’s skull as he nestled his head against his ribcage. The smell of his clothes, even if they were different clothes. The warm thrum of his soul.

The warm thrum Sans had never, _never_ thought he would feel again.

“It’s still your brother, Sans,” Gaster said, in such a reasonable, familiar tone that Sans came so close to believing him. “Just a different version.”

Sans stumbled even as he stood still. He brought his hands to his skull and dug his fingers into the bone. His breathing sped up, and his vision swam.

“that’s not my … he … that’s not my brother. _that’s not my brother._ he didn’t … he …”

Gaster sighed. “It’s still him—”

“no it’s _not_! ” Sans threw his arms out to his sides and stalked forward, teeth gritted, browbone low. “he’s _not_ the same papyrus, he’s not _our_ papyrus! he doesn’t … just because you were _born_ the same doesn’t mean you _are_ the same! all the stuff that happened to us growing up, everything we went through, he doesn’t … he’ll never … that’s not him. _that’s not him_! everything that made him who he was, all our memories, every moment we spent together, he … ”

He stopped five feet away from where Gaster sat, still not looking at him, just staring down at the papers in front of him like Sans had never moved. Sans swayed on his feet, but steadied himself, shaking his head again, slower this time. His breath came even faster, he felt hot all over, and he glared Gaster down with dark sockets, even though his voice came out far more pained than like any sort of threat.

“that’s not my brother,” he bit out. “ _that’s not your son._ how can you call yourself his _father_ when you think you can just go into some other universe and pluck out another version of him to _replace_ the one you had? how can you even _think_ that’s the same? how can you—”

“I just wanted my son back!”

Sans didn’t move. He didn’t speak. All the words that had built up in his throat faded away.

Gaster gripped the table before yanking his arms away and wrapping them around himself. Like Papyrus had when he was scared and didn’t want to admit it. His body trembled, and he sucked in a breath so shaky Sans could hear the tears unshed in his throat. He shook his head.

“I… I can’t lose him, I …”

His voice trembled and broke off, his eyes locked on the floor, wide and terrified and he had never looked so young and so old all at once. Sans had seen him afraid before. So many times, even if it was hard to imagine the man who had tortured both his sons being scared of anything now.

This was his dad. This was his dad when Sans had almost waddled off the edge of a cliff and into a lava pit. This was his dad when Papyrus broke his leg. This was his dad every time he made a stupid mistake in the lab and one of them got hurt, even in a minor way.

This was his dad when the machine meant to fix his eye almost killed him.

This was his dad as he conducted that first real experiment.

This was his dad before Sans had pushed him, and he had fallen, so far that Sans didn’t even know where he had gone.

This was who he wanted to get back. Who he had tried so hard to …

But not like this.

_Not like this._

Sans tried to make his voice work, he tried to look at Gaster and tell him that they couldn’t do this, even if he wouldn’t listen, they had to send him back, he couldn’t stay here, this wasn’t his universe, they couldn’t just go into another universe and steal their Papyrus and go on like nothing had happened. But …

If he went back … if they sent him back to the universe he had come from …

He would be gone.

He would be gone _forever._

The Papyrus here was just … he was dust, Sans couldn’t bring him back, he couldn’t bring back the dead, but there were others, there were so many others and one … just _one_ …

But that one wasn’t … he wasn’t _their_ Papyrus. He didn’t have the same memories, he dressed different, he talked different, chances were he was different in a thousand other little ways Sans hadn’t even noticed yet. But …

He was here.

He was alive.

Sans could protect him.

He could make sure no one ever hurt him again.

And Gaster …

He couldn’t hurt him again. He _wouldn’t_ hurt him again. Not after he had lost him, things would be different now, they had to be different now, it was … it wasn’t what he wanted, he wanted his brother, he wanted his dad like he had been before, but this … if it was all he had, all he could get, could he …?

His eyes flicked up and locked on the man across the room.

“what does it do?”

Gaster lifted his head to face him again, blinking, as if the words didn’t make sense. “Pardon?”

“the machine,” Sans replied, his voice blank even as his chest twisted and his head continued to spin. “you said it … stays at exactly the same point in all universes.”

Gaster straightened.

“Yes.”

“what does that mean?”

Gaster stared at him, half of his browbone barely raised. Even at his worst moments, he had never looked quite so condescending.

“I would think it would be simple for you, considering how many years you spent studying this.”

“well, pretend for a second that we don’t share a mind,” Sans snapped, resisting the urge to curl his hands into fists.

Gaster’s face softened, just a bit, before he looked away again.

“It’s exactly as I said, Sans. Your machine exists in the same point in space no matter which universe you visit,” he replied. Sans gave him an expectant look. Gaster ignored him. “It sticks. It _stays._ ”

Sans kept on staring. But Gaster was back to looking at the floor. He looked … distant, like he was still figuring this out himself. Maybe he was. If he had only tried to use it for the first time last night, if he had only _confirmed_ any of this without a matter of hours …

“While everything else shifts between universes, depending on what has happened, how they have split off, the differences, small or large, between them, your machine remains the same. You step into it in one universe, activate it, and when you step out, you are in another universe. In the _exact same spot_ in another universe.”

Gaster tilted his head just enough to meet Sans’s eyes, an expression on his own face Sans didn’t know how to read.

“Your machine refuses to change, refuses to disappear, no matter how many universes are crossed. Your machine remains stable when everything else shifts.”

It was clicking now. Slowly, like Sans’s mind wasn’t sure what to make of it. Even some of his most obscure, theoretical studies had been based on facts, on numerical values, on something … measurable, even if it was vague. But this … they hadn’t planned for this. Or at least, _he_ hadn’t planned for this. Maybe Gaster had. Who knew how many changes he had been making along the way, who knew what he had been trying to do, he hadn’t been _sabotaging_ Sans’s plans, but … he couldn’t have predicted this. He couldn’t have predicted needing to use it like this. And the longer Sans looked a him now, the more sure of that he was.

But it had still happened. And now, rather than trying to come up with a method to reach an end, it was left to them to figure out how they had gotten to this end in the first place, and what the hell it meant.

Gaster let out a soft breath, snapping Sans’s attention back to him.

“Put as simply as possible, your machine is … stubborn. It’s … determined,” he finished. “It exists everywhere at once.”

Sans’s browbone creased, even as the tension in his shoulders slipped away, and the last of the puzzle pieces began to click into place. The S.E. that made him stronger, not in the normal way, but strong enough to hurt Gaster when he didn’t have enough attack strength, strong enough to make his soul persist long after other monster souls would have turned to dust. The S.E. that he had stuffed into the machine on a whim, bit by bit, that had made all his readings fluctuate, that had honed in on part of a physical plane and … locked it in. Even when the universe around it changed.

Gaster gave a small nod as Sans met his eyes again, his own face still blank, yet churning with too many emotions for Sans to name.

“And by its simple, static existence, it creates a bridge between our universe and all the others.”


	41. Chapter 34

**Notes for the Chapter:**

> ... I've got nothing else to say. (But really, thank you for sticking with me.)

Sans wasn’t entirely sure when he had sat down. It was funny. After all that had happened, after everything he had heard, everything he had seen … nothing should have been a surprise to him anymore. But this was. Apparently.

Or maybe he was just tired.

He wasn’t sure how much sleep he had gotten lately.

He sat a good eight feet away from Gaster, close enough to see his expressions and hear his voice but not close enough to feel like his personal bubble was being invaded. Was his personal bubble that big before? Or was it just Gaster? How long had it been since anyone but Gaster or his brother had been close enough for him to even _think_ of a personal bubble?

Except the human.

Did she count?

Papyrus would have thought so. He would have insisted she counted just as much as any other person. She was human, but she was _alive,_ she had thoughts and feelings and he had barely known her but he had cared about her and she was …

Papyrus was …

Gaster let out a soft breath, and Sans’s attention snapped back up to him just as he began to speak.

“Parallel universe theory suggests that there are an infinite number of other realities existing alongside our own, some close to identical, some—”

“i have my _phd_ in this, gaster, stop playing professor and get on with it already,” Sans spat, crossing his arms so tight over his chest that his fingers almost got lost in his ribcage.

Gaster just looked at him for a moment, unimpressed. It was the sort of look Sans had seen on a few other parents’ faces in their more exasperated moments. But never on Gaster’s. Not when Sans would have still called him “Dad.” At last, he turned away again, as if Sans had never spoken at all.

“There may indeed be infinite universes,” he went on. “But … those universes are very distant from ours. And I believe there are a more finite number of them far closer, stemming from various branches but all beginning at one finite point. Otherwise, given that I was inputting coordinates into the machine at random, I would have ended up in universes where the world around me was completely unrecognizable, if there was anything in that exact point in spacetime at all. But instead, the places I visited were similar to our own. I stopped counting, but I believe I visited less than fifty before I found … Papyrus.”

He paused, as if even he couldn’t quite bring himself to call the skeleton back at their house the same person as his son. Despite it all, Sans allowed himself a brief moment of satisfaction, forcing back the little voice in his head that reminded him that the “Papyrus” back at their house was the only Papyrus he had now. The only brother he would ever have again.

The brother he wasn’t willing to give up.

He huffed a sigh.

“okay, so … what the hell’s supposed to have caused all those universes, then?”

Gaster looked at him without turning his head.

“As you said, Sans. You’re the one with the PhD in this area. And given that you were researching time travel, you must have considered the implications.”

Of course he had. It was one of the first things he had thought of before he built the machine. It was what lingered in the back of his head through it all, what reminded him that even if he did succeed, he might not _really_ succeed. He might succeed for his own sake, but not for the sake’s of those he wanted so badly to protect.

“you think someone … went back in time.”

“And each time they did, another universe branched off,” Gaster finished, and Sans hated the hint of almost-paternal _pride_ he could pick out in his tone.

Sans’s browbone furrowed. “you said you found at least fifty.”

Gaster hummed in assent.

“And I suspect there were dozens more. Hundreds, if not thousands.”

“you think one person went back in time that many times,” Sans said.

“Perhaps,” Gaster replied, though not very convincingly. He clasped his hands together and brought them close to his chin. “But I believe it was most likely more. Not a lot more, this sort of ability would undoubtedly have been noticed by now if it were this common, but … more than one.”

Sans didn’t think he had felt this thrown by a piece of information since he had snuck into an organic chemistry course when he was eight.

“you think other people built … time machines?” he went on, slower, as if that might make Gaster make the answer more sensible.

Gaster didn’t reply at first, and Sans let his mind drift, searching for his own response. Who the hell could have managed something like that? Well, even if he couldn’t imagine it now, even if a time machine, for him, was an enormous task he wasn’t even sure _he_ could complete, that didn’t mean that it wouldn’t be plausible someday. They could have been from the future. At any point in the future. All they would have to do is go back far enough in the past, and it would create a whole new universe. There could be a whole group of people, scientists, maybe, who had gone into the past to change something and—

“I don’t think they used machines.”

Sans’s head snapped up again, and it took several seconds for Gaster’s words to register in his head.

“what?” he muttered. His browbone furrowed. “then … how the hell did they go back in time without a machine?”

Gaster didn’t look at him, staring instead across the room at one of the blank walls. He didn’t seem to be avoiding Sans’s gaze intentionally, and Sans found himself looking at the wall, as if there might actually be something there to see.

“I tried a few things with your machine before I came into the lab today,” Gaster said at last. “In particular, I tried removing the S.E. core you put in. And as soon as that core was removed, the machine completely failed to function.”

Something deep in Sans wanted to say something else about screwing around with other people’s machinery, but he couldn’t bring himself to speak. He was far more busy processing what Gaster had said, connecting the dots even as he continued to talk.

“The S.E. is an essential ingredient to allow travel between the universes. But it isn’t all that’s required. I tried it when I first went to the lab last night, and nothing happened. Not until I added in some of the soul.”

Sans tensed, but did not speak. If Gaster noticed, he said nothing.

“The soul is a requirement, just like the S.E. Both are required to allow your machine to be more … solid, more permanent, more … _determined_ to exist in every universe, or at least a great deal of universes, at once.”

He turned his head to look at Sans again, and there was something in his eyes that made Sans shiver, even though he had seen a form of it dozens of times over the past few weeks.

“Whatever gave that machine the ability to travel between universes … theoretically, might also give it the ability to travel along a given timeline, therefore creating a new universe each time the user went back.”

Sans stared. Then he stared more. But Gaster said nothing else, and Sans’s mind already had the answer, even if it took him more than a minute to bring it to his mouth.

“humans,” he said, a tiny crease in his forehead. “you think … humans … can go back in time? with something that’s already … inside their souls?”

Gaster said nothing, but he didn’t need to. His expression was all the answer Sans needed.

Sans huffed and shook his head.

“but … you lived on the surface. you _knew_ humans. was that something they talked about? something they knew about? if they didn’t need scientific knowledge, if they didn’t need a machine, if they could just _go back in time at will_ —”

“No, I don’t believe they could,” Gaster cut him off, looking back to the wall. He paused, as if to sort out his thoughts. “Of course, there is no guarantee. They might have done it a million times and if they never mentioned it, we monsters would never have known. But I don’t believe it was a normal ability for humans. Not at that time, in any case.”

Sans stared. He was saying something, in the way he tended to say things when his mind was running a thousand miles an hour: without actually saying them, but giving Sans just enough so he could reach the same conclusion himself.

He took a step closer, his browbone scrunched.

“you said that you thought all the timelines you found linked back to one original point,” he said, as the pieces began to click together in his head, not all of them, not all the way, but enough for him to see where this was going. “what point?”

Gaster pressed his mouth into a thin line. “There is no way of being sure.”

“but you have an idea,” Sans replied.

Gaster didn’t say anything for a long time after that. Sans wanted to throw something at his head to get him to speak—though, frankly, he would have liked to throw something at his head anyway. Everything was screwed up, everything was wrong, he couldn’t think, he didn’t know what to feel, he didn’t know how to deal with _any_ of this, and it was _all Gaster’s fault._

At last, Gaster closed his eyes and sighed.

“You’ve heard the story of the first human to fall into the Underground, haven’t you?”

Sans’s mind stuttered again. His browbone furrowed.

“not since i was a kid,” he replied. His smile twisted into something like a grimace. “it’s … not something people talked about a lot in college.”

Gaster looked at him. “They died. Almost a century ago now.”

“uh-huh.”

Gaster paused, just staring back at him, as if, if he stared long enough, Sans would know exactly what he wanted to say. Sans just stared back, silent. Gaster’s mouth pressed into a tight line.

“They were alive.”

Sans’s browbone smoothed over. His sockets grew. Gaster looked down at his hands, clasped neatly in his lap, exactly as he had clasped them for as long as Sans could remember.

“In one of those universes, I saw them. Or … I heard reference to them. Old and bedridden and very close to death, but they were still alive,” he said. “As was the prince. Ruling alongside them.”

Neither of them spoke for more than half a minute after that. Gaster almost looked shaken, and for the first time in a long while, Sans realized that Gaster had been alive when that first human fell. He had visited the king a few times for important affairs, and the king was known for being personable. Maybe he had met them. Maybe he had known them. Maybe he had been one of the many monsters—from what Sans had heard—who had mourned their death just as intensely as the prince’s, though if Gaster had hated humans back then as much as he did now …

The prince had only died because he took their body up to the Surface. If they had survived … if they had failed once, then gone back and _made sure_ they would survive …

“you think it was them,” Sans breathed.

“One of them,” Gaster went on, lifting his head, his brief moment of unreadable emotions forgotten. “I believe they may have been the first. But, if there were others after them …”

He didn’t need to finish, if he had ever planned to. The pieces had already begun to click into place in Sans’s head. He just didn’t want to think about it.

“five more. five more humans,” he breathed, his browbone raised, his eyes tilting toward the ground. They flicked across the room, to the empty examination table, to the spot where that tiny body had lain for days. “six.”

Gaster didn’t say anything. Sans shook his head, his hands curling into fists at his sides.

“but how did they … what are the chances that all the humans that happened to be able to _go back in time_ fell down here?”

“I don’t believe it was chance,” Gaster replied. Sans just stared. Gaster turned away, staring up at the ceiling in something that, if Sans had been thinking a little straighter, he might have called nostalgia. “Humans … once had their own magical capabilities, though those seem to have faded since the barrier was constructed. There is no sign that any humans who have fallen have the same magical abilities as their ancestors.”

Sans searched his expression for something that might give him more of a hint as to what Gaster was remembering, but of course, he found nothing. And a second later, that expression disappeared, and Gaster looked down at his own hand, twisting it in front of him, as if examining one of his old experiments.

“However … monsters have always had a different sort of magic than humans. We’re made of it, after all, and it was only a part of them. And while monsters came in contact with humans quite often before the war, they were never in such close, constant contact with each other. Not for my entire lifetime, at least. And there has never been a time when so many monsters—and all their magic—was concentrated in one small location, as it is now, in the Underground.”

Sans could already see where this was going. And Gaster must have known that. He turned to him, watching him with expectant eyes, but Sans said nothing.

“There’s no way to be sure, or to test my hypothesis,” Gaster went on, after a long pause. “But if a human, with the innate … essence in their soul that could give them the power to return to past points in time at will … perhaps sudden and extreme exposure to foreign magical energy would combine with that essence and … trigger their abilities.”

“humans with monster magic,” Sans said, as much to himself as to Gaster.

Gaster nodded, a flicker of satisfaction in his eyes. “It was said that a monster soul and a human soul combined would create a creature more powerful than any of us could imagine. And though falling into the underground might not produce quite the same effect, it might be enough.”

It sounded ridiculous. But … all of this sounded ridiculous. How long had it been since he and Alphys discovered actual evidence of parallel universes, something he had assumed would remain only a theory for the rest of his life? How long had it been since he watched how a simple substance extracted from a human soul could change a monster?

 _Had_ changed a monster.

Had changed two.

“enough to … go back in time,” he finished, a tiny crease in his browbone. “whenever they wanted.”

“Yes,” Gaster said, though his attention seemed to have drifted back to his own thoughts.

Sans brought his arms a little closer to his body, almost close enough to count as squeezing himself like Papyrus—and Gaster—had done.

Humans could … go back in time. Or at least some humans had. Just by falling into the underground and exposing themselves to the high density of magic monsters had never even noticed at all.

The first human. That human kid, they … had they been able to go back? Could they still go back if they were dead?

They must have been. If there was more than one timeline where that first human kid had died, if there had been other timelines where they had _lived,_ they must have been able to come back. To try again. To go back in time and do things a little differently.

So the human kid _he_ killed …

… had she gone back?

After he killed her, had she gone back, maybe just a few minutes, maybe to before she were captured, maybe to when she first fell into the Underground? Had she learned from her mistakes? Had she kept dying and found every monster’s weakness one by one and—

Had she kept killing Papyrus?

How many times had she killed his brother?

How many timelines were there where his brother was dead? How many timelines were there when she had learned to avoid his attack, where she had learned exactly what he was going to do so she could do something different? So she could kill him, too?

So she could … how many people had she _killed_?

How many times had he failed to stop her from getting out? She was angry, she was scared, she was desperate, maybe she hadn’t been as big a threat before, but she had killed his _brother,_ the one trying to _help_ her, if she could kill him, she could kill _anyone._ As many monsters as she needed to get out.

Had the time he had met her even been her first time around? She hadn’t looked like she had seen his house before, but had she met Papyrus? Had she _hurt_ Papyrus before she realized he was harmless? Was there another universe out there when Papyrus had been turned to dust when he found her and there was _nothing Sans could do to protect him and_ —

There was nothing he could do.

That kid could go through infinite timelines and kill his brother over and over, she could kill everyone, and …

He couldn’t do anything. He could fight back against her a million times, he could stop her a million times, and she could still …

It wasn’t his universe, but …

Neither was the Papyrus in his house right now. Neither was the Papyrus he had clung to this morning, the closest thing to his brother he had left, the closest he would _ever_ have now that his Papyrus was—

There were hundreds of Papyruses, hundreds, if not more, versions of his brother, hundreds of versions of his entire _world_. And he couldn’t do a damn thing to protect them. Not when a stupid human _kid_ could go back on a whim and create more and more of them, doing whatever they pleased, playing with their lives like … puppets.

He could try as hard as he wanted.

And even if he succeeded once, there would still be hundreds of more times where he failed.

Sans’s head rose as his mind began to refocus on the world around him. Gaster was talking—rambling, by the sound of it—pacing back and forth and ranting on like he did in the midst of one of his more passionate projects.

“—and find another suitable container, I don’t know if what we have on hand will suffice—”

“what are you going on about?” Sans cut him off, his tone biting, yet quiet.

Gaster looked at him for a moment, like he had lost his mind. A touch of frustration flashed across his face. A second later, it was gone.

“Going back to the other universes,” he said, as if it should have been obvious.

Sans just stared. “what for?”

Gaster stared back. Both of them must have looked like the other one was completely insane, and Sans was just waiting for Gaster to realize that it was him. At last, Gaster let out a sigh and shook his head.

“Sans, I can understand that your mental state is less than ideal, but please, try to keep up,” he said, and Sans couldn’t help the faint flinch at his tone. “Going to the other universes to gather the human souls.”

A second ticked by. Two. Three. Four.

“… what?”

“If there are indeed as many universes as I suspect, then certainly in _one_ of them, if not most, they have souls already collected,” Gaster went on, apparently talking more to himself than to Sans. “We wouldn’t even have to fight humans to get the souls, and the containers would be provided, we wouldn’t have to search for some here and lug them around with us. All we would have to do is find out where the king is keeping them, get there without detection, and—”

“wait, wait, _hold it,_ ” Sans cut in. Gaster turned to face him, browbone furrowed. Sans stare, trying to process what he had heard, trying to figure out what the hell he could say in response. He shook his head. “we just discovered all these parallel universes and you just wanna go … take the human souls they’ve got?”

Gaster looked at him with the same expression as before, the expression of a madman wondering why everyone else had lost their heads. “All we need is two, Sans. Two, and we’re out of here. You and Papyrus won’t have to go through any more experiments. Two, and it’s _done._ Though I imagine it would be a good idea to take three or four, just to be safe, to help us avoid having to go back.”

Sans floundered for a few seconds, gesturing with his hands as if that would help him get the words right.

“but … that would set them back who _knows_ how long.”

“We can’t worry about what happens to every single one of these parallel universes, Sans,” Gaster replied, his browbone creased once again.

Sans’s sockets had never felt so wide in his life. “we can if we’re _stealing from them!_ ”

Gaster said something in response, but Sans wasn’t listening. All he could hear was his own words echoing in his head. Stealing. They weren’t just stealing things, they weren’t just stealing _souls._ They were stealing _people._

Papyrus. The Papyrus was who was in their house right now.

Gaster said he knew who Sans was. He was used to him being there, he had been born, he hadn’t died. There was a Sans out there, in another universe, whose brother had been snatched up and dropped in another universe.

And the other him would never know.

He would look for his brother, without a doubt. He would search everywhere in the underground, probably five times over. And he wouldn’t stop then. He would keep looking, he would spend the rest of his life searching, he wouldn’t even have the closure of his brother being _dead,_ he would have to live on _hope,_ hope that his brother was still alive, hope that he could see him again, hope that would never get him _anywhere._

And Papyrus … the Papyrus who had held him this morning, the Papyrus who had shoved protein bars into his hands, the Papyrus who rambled on and wore different clothes and said strange things but he was _so like Papyrus that Sans couldn’t bear to think of letting him go—_

That wasn’t his brother.

But … it _was_ his brother. And if Sans gave him back, if Sans _lost_ him …

He would never …

 _His_ Papyrus would never …

He looked at Gaster, but Gaster was no longer looking at him. He had turned back to the notes on his desk, apparently given up on convincing him of what he was doing—or maybe he had never cared in the first place. Sans couldn’t remember the last time Gaster had genuinely cared about his opinion.

He wouldn’t listen to him.

Sans was sure of that.

He could say whatever he wanted. He could scream until his voice died. Gaster wouldn’t hear him.

He would go through with it.

He would go to one of those other universes and take away what little hope they had, just so he could get what he wanted.

Just so he could … set them all free.

If he could take a person, his _son,_ from another world, what was a few souls?

And then … and then …

Then what?

They would be free. They would really get out of here. That other universe would be screwed over, but _they_ would get out of here. They would have all the souls they needed to get out of here, once and for all.

His da—Gaster wouldn’t have any reason to continue the experiments.

But Sans wouldn’t get him back. He knew that now. He was never, ever going to get him back.

And his brother …

They would get what they wanted. They would get what all monsters had wanted for so goddamn long.

And he still would have lost everything that mattered.

He let himself sink down into a nearby chair, so fast it almost rolled into a desk. He didn’t care, and Gaster didn’t notice.

Gaster wrote, and Sans sat in a silence so thick he swore he was drowning, with no energy left to swim.


	42. Chapter 35

**Notes for the Chapter:**

> Might be a few more questions answered here ... and probably a few more asked, too.

Sans stayed at the lab for the rest of the day.

He didn’t want to stay. He wanted to go home, he wanted to get away from all of this, he wanted to lay down on his bed and hide his face in his pillow and forget all of this had happened. He wanted to go home and find his dad and Papyrus sitting at the dinner table with some elaborate meal laid out in front of them. He wanted to talk about his day and listen to Papyrus ramble on about his and try to get his dad to tell him what sort of crazy experiment he had thought up next.

Maybe icy bracelets. Working on the icy bracelets sounded really good right now.

Why had he ever thought the idea was dumb?

Icy bracelets were the best damn idea he had ever heard of.

If he worked on nothing but icy bracelets for the rest of his life, with his dad by his side and Papyrus smiling and happy and alive and safe and _him,_ he would be happy.

But despite how much he wanted to leave, Sans stayed, if only because he couldn’t seem to make his legs move steadily enough to get him all the way back to the house. Gaster said nothing to him. He sat at his desk, writing—something lengthy and important, by the looks of it, though Sans didn’t pay much attention. Only when the clock struck five did Sans finally force himself to climb off his chair.

Papyrus would be waiting for him. He would worry if Sans didn’t show up.

Or would he?

Did this Papyrus care if his brother got home late?

He started toward the door, but before he could reach it, his eyes flicked toward a small table by the wall. A table holding a single glass container, with something yellow glowing inside.

He hadn’t noticed it when he came in, but there it was. Just like Gaster had said. A piece of a human soul, completely intact. Set to the side, like it no longer mattered.

It wasn’t going to help them get out of here. It wasn’t a whole soul, not even half a soul, but it was still a _soul._ A piece of a soul they could have used for the barrier, if Gaster hadn’t used it for—

But if he hadn’t, Papyrus …

Sans glanced over his shoulder, and found Gaster still hunched over his notes, scribbling away like before. He took a step toward the table, then another, and another, and Gaster didn’t so much as twitch.

Then he reached out and snatched the container up.

Gaster didn’t even look his way.

Sans slipped the container into his bag and scurried out the door, not even pausing to breathe until he had gotten up to the ground floor and out of the building.

It was a miracle he didn’t fall into a lava pit or walk into a wall from how little attention he paid to his surroundings. He had done that before—the wall, not the lava—when he was in deep thought, contemplating some new project or idea. He wasn’t thinking now. He didn’t want to think. He wanted to go to sleep and never, ever wake up.

Would Gaster come find another him, if he died?

Would it matter, like Papyrus had mattered?

Would he find it so easy to replace him with another Sans, like he had picked out a new Papyrus, like he was replacing a broken toy?

Would he miss him?

Did he miss Papyrus?

The thoughts churned in his head, so fast he could barely decipher them, as he walked the rest of the way home. He barely noticed when the house came into view, barely felt himself pulling the key out of his pocket and turning it in the lock. Only when the door opened and he caught a hint of movement across the living room, in the entrance to the kitchen, did he finally look up.

There was Papyrus.

 _A_ Papyrus.

Not …

Sans swallowed as Papyrus turned to face him, wearing the same apron Sans had watched his brother put on almost every evening for years. Did he have an apron like that, too? Was that why he was wearing it? Or had he just seen it and thought he might as well wear it while he was in the kitchen?

“THERE YOU ARE!” he said, putting his hands on his hips. Was that really how he talked all the time? Papyrus had always been a little louder than most people, more enthusiastic, but … “I WAS JUST ABOUT TO COME LOOKING FOR YOU. DINNER IS READY!”

For the first time, Sans noticed the plates laid out on the table.

Two plates.

Papyrus had always made three plates. Even when he was fairly sure that Gaster wouldn’t be there, he still made three, if only so their dad would have something to eat out of the fridge once he got home. There was a chance that he had already put the plate in the fridge, but somehow, Sans felt like that wasn’t the case. He didn’t know why. Maybe because Papyrus didn’t even bother to glance toward the door, as he always had, to check that Gaster wasn’t behind him.

“thanks, bro,” Sans forced out nonetheless, flashing a smile even he didn’t believe.

Without waiting to see Papyrus’s response, he took a seat in his normal spot in front of one of the plates, while Papyrus took the other. Sans glanced across the table to watch Papyrus pick up his fork and begin eating. He ate the same. Held his fork the same. Chewed the same. Or was that just Sans’s mind playing tricks on him? It wasn’t like he had ever paid much attention to those little details. Maybe it was completely different.

He would never know.

He could never go back to see.

Sans scooped up some of the food—some kind of noodle dish, by the looks of it—onto his fork without thinking about it. He watched Papyrus eat for a few more seconds, taking in all the tiny nuances of his movements, checking them against his memories as if that might actually give him answers. It didn’t. He let his eyes drift back to the table. Then put the fork to his teeth.

His whole body stiffened. His sockets went wide.

And he had to fight every instinct not to spit it out then and there.

It was … he didn’t even know how to describe it. Spicy yet bitter and sweet and savory all at once, he knew Papyrus liked to experiment but this wasn’t an experiment, this was an _abomination._ For a second, he thought this Papyrus had realized he was in the wrong universe and had put something in his food to drug him or kill him, but no, it didn’t matter what universe this was, this was _Papyrus,_ he would never do something like that but _damnit did it taste like it._

He looked up just in time to see Papyrus beaming at him from across the table.

“YOUR EXPRESSION IS EVEN MORE PASSIONATE THAN USUAL, SANS! IT MUST HAVE BEEN A REALLY GOOD BATCH THIS TIME!”

Passionate.

Was that what his face looked like right now?

After a few more seconds and a rush of willpower, Sans swallowed, squeezing his sockets shut to clear them before looking back to his brother. Papyrus, thankfully, had already started digging into his own food. Either he didn’t notice the taste, or this truly was something he enjoyed.

Oddly enough, he hadn’t considered that a Papyrus from another universe would have different tastes than his own.

Or … maybe not any sense of taste at all.

It had been a long, long time since Papyrus first learned how to cook, and Sans couldn’t be sure that his food hadn’t tasted like this early on. But he remembered taste-testing it, and he was quite sure he hadn’t wished this desperately that he had gotten a glass of water to have with dinner.

At first, he was afraid that he would have to take another bite to appease his brother, but Papyrus, to his relief, just went back to his own food, making contemplative faces after each bite which might have been appreciative and might have been disgusted for how little Sans could read them. Sans took to pushing his food around with his fork. That had never worked before—on those rare evenings when he was so anxious about schoolwork that he couldn’t bring himself to eat—but today, Papyrus didn’t say a word.

Several minutes passed in silence, broken only by the clinking of silverware on plates. Then Sans set down his fork and cleared his throat, just loud enough to make out.

“so … did gaster stick around long this morning?”

Papyrus looked up, a little startled, before his browbone rose in comprehension.

“OH, THAT TALL SKELETON? HE WAS AROUND FOR A FEW MINUTES, BUT HE LEFT JUST AFTER I WOKE UP. IS HE COMING BACK FOR DINNER?”

“don’t think so,” Sans muttered, without really thinking about it.

Papyrus paused, but didn’t go back to his food. His mouth pressed into a tight, twisted line, like it did when he was thinking—or, at least, like _his_ Papyrus had when he was thinking.

“HE’S VERY QUIET,” he said at last. Then he broke into a wide grin, his temporary anxiety apparently forgotten. “BUT HE’S VERY HOSPITABLE! I’VE NEVER MET SOMEONE WHO WOULD SET UP TWO WHOLE BEDROOMS FOR THEIR GUESTS ON SUCH SHORT NOTICE.”

Sans tried not to let his confusion show. He allowed the latest bits of information to settle into the messy, uneven puzzle of all the questions that remained unanswered, and waited a good half-minute before he cleared his throat.

“so he said we’re guests?”

Papyrus hesitated again, a crease on his brow. “WELL, I SUPPOSE I’M HIS GUEST, SINCE I DON’T KNOW HIM,” He tilted his head. “ARE YOU STILL HIS GUEST? OR JUST HIS FRIEND WHO SLEEPS OVER SOMETIMES? HE SAID YOU’VE KNOWN EACH OTHER FOR A WHILE AT YOUR JOB. I DIDN’T KNOW YOU HAD ANY CO-WORKERS AT THE SENTRY STATION. YOU NEVER TOLD ME ABOUT HIM.”

He looked at Sans, and Sans averted his gaze. He wasn’t sure how good his lying would be at this point—or how well this Papyrus was at reading his cues. He shifted in his chair, picking up his fork and poking at his food, though he had no intention of eating another bite. Maybe he could throw something together later. Or heat up a frozen dinner. Or … well. He wasn’t really that hungry anyway.

Finally, he shrugged.

“yeah, he … we see each other sometimes.”

When he dared to look back up, he found Papyrus frowning down at his plate, eating apparently just as uninteresting to him as it was to Sans.

“IT’S VERY STRANGE,” he said, as if to himself. “I DON’T EVEN REMEMBER HOW I GOT HERE. WHEN I WOKE UP, I WAS IN A ROOM THAT _LOOKED_ LIKE MY ROOM BUT … WASN’T. AND I LOOKED OUTSIDE AND IT WAS HOTLAND AND I WAS EVEN _MORE_ CONFUSED AND THEN THAT STRANGE GASTER-SKELETON TOLD ME WE WERE STAYING WITH HIM FOR A FEW DAYS BECAUSE SOMETHING HAPPENED TO OUR HOUSE. HE WAS VERY QUIET AND … SHIFTY, BUT THEN I WENT UPSTAIRS AND SAW YOU IN YOUR ROOM, BEING A LAZYBONES AS USUAL, AND I THOUGHT I’D JUST ASK YOU WHEN YOU WOKE UP.”

He looked up at Sans, and Sans barely managed to force his expression back into something neutral—or at least something that could pass as neutral. Papyrus’s browbone furrowed further, in something Sans could just recognize as concern.

“THEN YOU WERE ALL HUGGY AND UPSET THIS MORNING. IS IT ABOUT WHAT HAPPENED TO OUR HOUSE? WHAT _DID_ HAPPEN TO OUR HOUSE? I WENT TO GO LOOK AT IT AND IT … WASN’T THERE.”

Sans face froze. Dammit. Damn it all to hell. His mind stuttered, and Papyrus kept staring, waiting, wondering, while Sans tried to sort any of this into a picture he could make sense of.

“where’d you look?” he managed at last, his voice little more than a croak.

Papyrus frowned.

“IN SNOWDIN, OF COURSE! GOD, SANS, DO YOU THINK THE HOUSE JUST GOT UP AND WALKED AWAY?” Then his frown softened, and he looked down at his plate in deep thought. “THOUGH I DON’T SEE ANY SIGNS OF IT … CAN HOUSES GROW LEGS WITHOUT YOU NOTICING? WE’VE LIVED IN THAT HOUSE A WHILE, I THOUGHT I WOULD HAVE NOTICED BY NOW.”

Sans cleared his throat in lieu of a response. Papyrus fidgeted, frowning again as he stared down at his lap.

“I COULDN’T FIND UNDYNE EITHER.”

For what must have been the fiftieth time that day, Sans was struck silent.

“undyne?”

Papyrus looked up once more, more exasperated than confused.

“YES. UNDYNE. YOU DIDN’T FORGET HER NAME, DID YOU, SANS?” he asked. Sans stared back, not even trying to put a convincing grin on his face. But Papyrus just groaned and shook his head. “YOU REALLY ARE A LAZYBONES. I’VE KNOWN HER FOR TEN YEARS AND YOU’VE SEEN HER PLENTY, YOU COULD AT LEAST _TRY_ TO REMEMBER WHAT SHE’S CALLED.”

He said it like he had said it a dozen times before, and Sans found himself wondering how forgetful his other self could be that he wouldn’t remember who Papyrus’s friends were.

Then again …

… when was the last time he had talked to his brother about his friends?

Not since he had started working at the lab … but before graduation, certainly. He must have. Of course, he had been busy with his exams, and even when he had been home, he had been distracted …

… where were Papyrus’s friends now?

Did they miss him? _Would_ they miss him?

When was the last time any of them had talked to him?

How many people in this Papyrus’s old world would know that he had disappeared?

“I LOOKED FOR HER HOUSE AND IT WASN’T THERE EITHER,” Papyrus went on, jerking Sans’s attention back to him. “AND I LOOKED NEARBY AND I COULDN’T FIND IT. AND I ASKED PEOPLE IF THEY HAD SEEN HER AND NONE OF THEM KNEW WHO SHE WAS.”

He looked away, frowning again.

“THEY KNEW WHO _I_ WAS, THOUGH. I DON’T KNOW WHY THEY WOULD FORGET JUST HER, WE’RE TOGETHER ALL THE TIME.”

His face twisted into something like distress, and Sans had to fight every instinct not to throw himself across the table and pull his brother into his arms. Papyrus should never look like that. And now Sans could talk to him again, he could help him, he could be there for him—

But this wasn’t …

… _this_ Papyrus …

“AND THEY KEPT ASKING ABOUT MY DAD.”

Sans’s thoughts crashed to a halt like they had run into a brick wall. He blinked, then stared at his brother. When had he started looking at him again? Papyrus tilted his head, browbone furrowed in genuine confusion.

“DO YOU THINK THEY KNEW HIM BEFORE HE DIED?” he asked, each of the words like another brick, plopping down from a crumbling ceiling onto his head. “YOU SAID YOU REMEMBER HIM A LITTLE, RIGHT? DID A LOT OF PEOPLE KNOW HIM?”

Sans couldn’t breathe. He couldn’t process the words flying around in his head. There was no grief on Papyrus’s face. Nothing that suggested he was missing someone he had known. Someone who had played any part in his life. Someone who had been around to care for him, to hold him, to read to him, to tuck him in, to carry him around.

Someone who had been around to hurt him.

“must have,” Sans managed, through his racing thoughts. He looked away. “i don’t … i don’t really remember much either.”

Papyrus stared at him for a few seconds, then hummed. “HUH. WEIRD.”

He paused, and Sans thought that he might ask something else. But he didn’t. He took another bite of his food and chewed, staring off into the distance, as if in thought.

He didn’t know. He hadn’t even guessed. Of course he wouldn’t. If his Gaster was dead … had he even known his name? What he looked like? Had there been any pictures? Or had that Gaster been as bad as this one, snapping pictures of his children left and right but never bothering to include himself in any of the photos?

Had they been old enough to know their dad as anything else but … “Dad”?

Papyrus hadn’t suspected anything so far. But … Sans might not have, either. It was ridiculous. It was far-fetched. Why would Papyrus suspect that he had been plucked out of his own universe and put into another where his dead dad was still alive?

And Sans didn’t want him to know.

Even if they had to send him—even if he couldn’t sta—he shouldn’t know. He _couldn’t_ know.

This wasn’t Papyrus’s father.

Sans didn’t _want_ this to be Papyrus’s father.

Whoever Papyrus’s real dad had been … chances were, he had been a hell of a lot better than this one.

And Sans didn’t want to risk even the slightest chance that this Papyrus would think that _his_ dad could become the man back at the lab.

He poked at his food a little more, glancing at Papyrus to find that he had stopped eating again, and had his eyes locked on the door, as if someone might come in at any second. A slight crease had formed in the center of his browbone.

“HE SEEMED UPSET ABOUT SOMETHING,” he went on. “THE GASTER-SKELETON WHO WAS HERE THIS MORNING.”

Sans’s soul twisted at his expression, but he said nothing. Papyrus looked back to him, his browbone tilted up, his mouth curved into a faint, almost knowing frown.

“DID SOMETHING BAD HAPPEN, SANS?”

It wasn’t a question. Not really. Sans knew when Papyrus was really asking questions, and it didn’t sound like that. Or at least … it hadn’t with his Papyrus. Was this one the same? Was he …?

How long could he keep thinking of this one as _not his Papyrus?_

If he stayed …

Papyrus was dead. But he was alive. Right in front of him. Staring at him, watching, waiting for an answer. And his clothes were different and his cooking was disgusting and there were all these little things that were _wrong_ about him but it was _still_ him and Sans couldn’t even think of letting him go.

Even if it meant he was stealing someone else’s brother away.

He cleared his throat and shook his head, trying to smile.

“nah, bro. it’s all good. he’s just weird.”

Papyrus didn’t say anything. He didn’t seem to _not_ believe Sans, but Sans wasn’t sure whether he believed him either. He just looked at him, for what felt like a very long time, until Sans finally gave in and glanced away.

Even with his eyes locked on the floor, he could still feel Papyrus’s gaze boring into him.

“ARE YOU UPSET ABOUT SOMETHING?”

His head snapped up, his sockets wide and blinking.

“huh?”

“YOU LOOKED UPSET, TOO,” Papyrus went on, still frowning, a little deeper now, and god, it was so much like his brother, he sounded _just like_ his brother when he was worried about him, but he couldn’t keep him and he couldn’t lose him and he … “WHEN YOU CAME BACK. AND YOU WERE UPSET THIS MORNING.”

Sans started to talk, then held himself back. Papyrus kept watching him, and bit by bit, the brief, impulsive words that tried to force themselves out of Sans’s mouth died down. He shook his head and tried to smile.

“don’t worry about it. everything’s fine now.”

Papyrus’s eyes didn’t leave him. He didn’t blink. He barely even seemed to breathe. His browbone furrowed deeper, his mouth set in a worried frown Sans had learned to read all too well.

He didn’t believe him.

But he didn’t say anything, just smiled and nodded and picked up his fork to take another bite. Sans gritted his teeth and stared down at his plate, pushing his food around a little more, even though he was beginning to doubt it was fooling Papyrus.

Neither of them spoke for the rest of dinner, and when Sans picked up the plates to take them to the sink, Papyrus didn’t protest.


	43. -8

He had met with the king once, when the prince was only a few years old.

He had seen the prince before, of course, as had the rest of the underground at the time. The king and queen had been all too proud to take him around to “meet” everyone when he was first born, even though he did little more than grab at people’s fingers and squirm and make noises. Gaster, of course, had been no exception. But after that, though the prince made plenty of “rounds” around Home, Gaster rarely saw him. He spent most of his time in his lab, after all, and a cluttered lab wasn’t exactly the safest place for a small monster, especially once he began to walk around on his own.

But Gaster still had to give his reports on the current status of scientific research—as little as was actually being accomplished in those days—and though he usually gave those reports in paper, sometimes the king insisted he come over for tea.

Gaster had always suspected that the king just wanted to get him out of the lab for half an hour.

He always accepted, of course, even though he still found long conversations uncomfortable without the ability to speak. The king was fluent in sign language, as was the entire royal family—a necessity for communicating with nonverbal monsters—and he tried to make it as easy for Gaster as he could.

They didn’t talk for very long, perhaps because the king was usually busy, and perhaps because Gaster preferred to avoid lengthy social situations—even if they were work-related. He went over the updates on his work as efficiently as possible, but the king always managed to keep him at least ten minutes longer than he really needed. Most of the time, those ten minutes were uneventful.

Sometimes, they weren’t.

Most notably, the first time the young prince had snuck up next to Gaster and, without warning, clambered onto his lap.

Gaster hadn’t even noticed him come into the room, and if the king had, he had said nothing about it. The first sign he got of the prince’s presence was a hand touching his leg, followed quickly by a second, hoisting the young child’s body up into lap. All Gaster could do was look down, wide-eyed, as the prince stared up at him and giggled, smile stretched all the way across his face.

It was the first time in at least a hundred years—if not a thousand—that he had seen a child this close.

And he couldn’t even remember if he had seen a boss monster child before.

The king was chuckling, but Gaster just stayed perfectly still as the child leaned forward to pat around his face, exploring the bone structure. When Gaster didn’t flinch or pull away when he neared his eyesockets, he carefully stuck a finger in one, then another, his own eyes growing wide and wondrous with every gesture. When he managed to stick his entire fist in without any negative effects, he giggled and clapped his little hands.

He looked across the table at the king, and the king smiled at him, his eyes fond and gentle, even more so than usual. Then the young prince climbed back off Gaster’s lap, gave him a quick wave, and toddled back out of the room, likely going to rejoin his mother, wherever she was at the moment.

Gaster blinked a few times, still as straight as a rod in his seat as he turned back to face the king. The king just laughed, shaking his head and tilting it to the side, toward the hall where his son had disappeared.

“They grow up so fast, don’t they?”

Gaster had nodded, on the sort of reflex that made him nod at anything he didn’t understand, but which he believed to be common knowledge.

He _didn’t_ know that they “grew up so fast.” Time didn’t seem to have passed by any faster over the past few years than it had before that—though, at his age, time did pass quite fast, compared to when he had been younger. It was the sort of thing he had heard parents say dozens of times—at least, from a distance, given how rarely he spoke to parents—but he couldn’t understand it. He had assumed, at the time, that he never would.

Looking back at his younger self now made him want to laugh.

It was like someone had drawn a line in his life eleven years ago. More than two thousand years of relative solitude, focusing solely on his work and his ambitions, and eleven years of … this. Whatever “this” was. He had no idea if his experience of parenthood, or family, was anything like what the king’s had been. It wasn’t like he was ever going to ask. But regardless of the differences, he still found himself glancing at photos of his boys eleven years ago and looking at them now and wondering if he could find scientific proof of time speeding up.

Papyrus had just started middle school a few weeks ago, and Sans had been in high school for well over a year. Gaster was used to it by now, in a way, and despite his advanced academics, it was easier to look at Sans as still a young child, given that he hadn’t hit his growth spurt, and Gaster was beginning to wonder if he was going to grow much more at all. Papyrus was another story. Though monster height varied tremendously—especially around the preteen years—Papyrus remained one of the tallest children in his class, and Gaster wouldn’t have been surprised if he turned out to be almost as tall as him, if not even taller.

He had heard rumors of the older kids teasing Sans that if he had had his brother’s physique, he might have been able to pass for someone their age.

Gaster still wasn’t sure whether Sans found the jokes funny.

Sans wouldn’t be in high school for much longer, though. There just weren’t enough classes left for him to take. He had only just had his eleventh birthday and he was already taking classes entirely with seniors, and by the time he turned twelve, he would have finished all the coursework required to graduate.

Graduate.

He would be moving on to university after this, wouldn’t he?

It shouldn’t have been this much of a shock. They had already discussed the idea of him attending college several times at dinner—and Gaster had known he would start early ever since he first started skipping grades. But that didn’t make it any easier to accept now that he really thought about it.

His son. Not even a teenager, and ready to start university.

If that wasn’t a prime example of “they grow up too fast,” he didn’t know what was.

He left work a little earlier than usual today, and found the house in sight just as everyone else began to get off of their own jobs. He had been staying late all week—all month, really—researching solutions for the dozens of problems arising with the Core. It was progressing relatively well, all things considered, but “relatively well” meant that it hadn’t yet exploded and no one had died in the construction, and it _was_ producing regular, clean energy, even if there was a significant malfunction at least once every few weeks. He had hoped to have a nice evening with both of the boys, but apparently Sans was sitting in on one of Alphys’s study groups, in the hopes of getting a head start on the university work he would be starting far too soon. So it would just be him and Papyrus until late that night.

Well. Maybe that was a good thing. It had been a while since he had spent time with Papyrus without his brother around.

He climbed the steps to the porch, unlocked the door, and walked into the house. Then he paused.

Papyrus wasn’t in the living room.

Papyrus was _always_ in the living room when he got home.

If he wasn’t there already, he was there within a few seconds, calling his name and running up to give him a hug and tell him about his day.

He wasn’t staying late today, was he? Gaster didn’t remember any social events. Besides, Gaster had mentioned he would be coming home a little early today, and Papyrus had seemed excited about it. He had even talked about them making dinner together. So where was he?

Gaster frowned, set his bag down near the door, and started up the stairs. He poked his head into Papyrus’s room—empty. Still immaculately clean, too, as it had been since he and Sans finally decided to get their own separate rooms on a trial basis six months before. Gaster checked his own room and Sans’s, but still found nothing.

Finally, frustration building to panic, he pushed the door open to his office and stepped inside.

And stopped.

With the mess covering most of the floor, it was hard to tell that anything was amiss at first glance. But even if he had been blind, Gaster couldn’t have missed the lanky little skeleton splayed out on his front in the middle of the floor, papers laid out in front of him, a box of crayons off to his side.

“Papyrus?” he asked, the name leaving his mouth before he had time to link.

Papyrus looked up, his hand pausing. In under a second, his face had lit up with a bright smile.

“Hi Dad!”

Gaster looked down at the papers, then back to Papyrus again. “What are you doing?”

Papyrus’s gaze followed Gaster’s. His smile shrunk, and when he looked up, his browbone was high in concern.

“Oh … was I not supposed to draw on these? I’m sorry …”

But Gaster barely heard the apology—not that he had been asking for one. Even if Papyrus had drawn on something important, it would have been Gaster’s fault for not telling him. No, his attention was far more intent on the paper at the top of the stack. He was fairly sure it was the back of one of his old reports, something irrelevant to current research based on the poor condition of the paper, but where there had once been blank white paper, there was now an elaborate picture in bright blue crayon.

At first, he thought it was just a random design made up of a lot of straight lines. An odd aesthetic choice for Papyrus, but nothing _that_ unusual. But he had spent far too much time staring at the blueprints of the Core not to notice the shape of it, particularly when it appeared that Papyrus had taken painstaking measures to ensure that it was accurate even scaled down.

But there were new lines there, too. Lines Gaster didn’t recognize. Lines that seemed to … separate parts of the Core. His browbone furrowed as he peered closer, and he noticed little arrows pointing in different directions. If he looked even closer, he could just make out other lines, drawn in different crayon colors, that looked like … other layouts. The same basic pieces, the same _Core,_ just … rearranged.

“What did you draw here?” he asked at last, looking back up to meet Papyrus’s eyes.

The hesitation slipped from Papyrus’s face, and he broke out into a grin.

“It’s a puzzle!”

Gaster blinked. He looked back down to the drawing, then to Papyrus again.

“The Core is a puzzle?”

“Uh-huh!” Papyrus replied, pushing himself to his feet and holding out the drawing so Gaster could see it more clearly. “You see, it’s made up of all these different pieces, and if you move them around like this and like that, you can mix it up! So it’s always brand new!”

Gaster’s eyes returned to the pattern as Papyrus’s fingers traced it out, and indeed, he found exactly that. All the pieces of the Core sliced up so that they could slide around at will. Of course, the Core _wasn’t_ made like a puzzle, and the pieces weren’t meant to move, but with this pattern, if some sort of mechanism was attached to allow each piece to shift …

“A puzzle,” he repeated.

Papyrus nodded, grinning even wider. “Yeah!”

Gaster took the paper in his own hands, and Papyrus let it go without complaint. He leaned in a little closer, taking in every detail, every arrow, every differently-colored line. He could already feel his mind pushing the pieces into place, he could already see the design plan, the construction details.

“Different pieces … moving around …” he murmured, more to himself than to anything. He stared a second longer. Then it clicked, so fast he almost dropped the paper in his shock. “That’s it!”

“Dad?” Papyrus asked, staring up at him with wide eyes and a furrowed browbone.

But Gaster barely heard him, his mind racing faster than it had in months, faster than it had since he had started this project six years ago. Filling in the blanks, translating the crayon drawing into blueprints, he could see it now, how could he not have _thought_ of it before?

“If they’re always moving around, they won’t overheat!” he burst out, his mouth curling into a grin, his eyes shining so bright he swore he could feel his magic flaring. “They’ll have a chance to cool off before anything warps.”

“Uh … yes?” Papyrus replied, tilting his head and blinking. He pushed himself to his feet and pointed at the bright red lines he had drawn around certain parts of the Core. “And you see, I made a map, so that’s how they can move around! Like a puzzle cube!”

Gaster nodded, faintly, finally lifting his eyes from the paper to meet his son’s eyes. “Yes. Yes, you did this perfectly.”

Papyrus turned to him, staring for a second before his face lit up in a wide, eager, yet almost disbelieving grin.

“I did?”

Gaster felt his smile fading, even as Papyrus’s smile grew, more and more hopeful by the second.

As if Gaster had given him something invaluable. As if he had just received the most incredible praise he could imagine.

As if he had never heard praise like it before.

And suddenly, it was like Gaster could hear all of his own words reflected back at him, everything he had said over the years, and the many, many things that he hadn’t.

He had never forgotten what Sans had told him, even if he tried not to think of it very often. He had never forgotten what he had seen in the behavior of those he knew, how their attitudes, their words, shifted so completely when they talked about Sans and when they talked about Papyrus. But as hard as it had hit him, as much as he had wanted to change it, he had never been sure what he could do.

His sons were different. There was no escaping that fact. Sans was going to university at twelve years old, and Gaster wasn’t even sure if Papyrus was interested in college, or if anything he wanted to do for a living would even require—or benefit from—a degree. And most of society, at least the people he knew, valued a job following a college degree far more than a job without one.

And so did he.

He had never thought about why. Maybe because he had always been the intellectual, he had always placed so much value on academic pursuits, even if it had been centuries since he had last sat in a classroom in a student’s role. But did that make any sense? Was it _fair_? Why should he value Sans’s science fair projects and physics studies more than Papyrus’s crayon drawings and improvised dance numbers and the dozens of little hobbies he picked up? What made one of them automatically better than the other? Sans didn’t seem to think his physics work was any better than a new drawing Papyrus spent days getting just right. So why did Gaster?

Was he so desperate to look only at the qualities in his sons that were similar to him that he had completely overlooked those that were different?

How many skeletons had been more like Papyrus than they had Gaster? How many skeletons had he overlooked because they weren’t like him, how many skeletons could he have taken the time to get to know if he hadn’t been so _stupid_?

How many years had he wasted valuing one of his children above the other, simply because they didn’t see the world, and what was important in it, the same way?

How much had it hurt when the skeletons he had called his family had failed to acknowledge his own talents and skills, just because they weren’t the same as theirs?

Gaster looked down at the paper, then back up to Papyrus. _His_ Papyrus. His son. His precious, unique son, who had solved a problem that had stumped every scientist who had worked at or visited the lab in the past six years, just because he wanted to draw a puzzle.

“Yes,” he breathed. “Yes, Papyrus, you did _marvelously._ ”

Papyrus’s whole face beamed, lighting up brighter than Gaster had seen it in years. Gaster’s eyes softened, and he allowed himself a moment to squeeze his son’s shoulder before he looked back to the paper in his hands.

Maybe what Papyrus had to offer wasn’t the same as his brother. But he was determined to help, determined to change things, determined to make the world a better place.

And one way or another, Gaster was sure he would.

**Notes for the Chapter:**

> Though I took my own spin on it, this idea is not originally mine. It was inspired by [this Tumblr post](https://drundertalescum.tumblr.com/post/153800660129/core-engineer-papyrus), so credit where credit's due!


	44. Chapter 36

**Notes for the Chapter:**

> IMPORTANT NOTICE: From now on, new chapters of _It's Raining Right Here_ , as well as the upcoming sequels (have I mentioned sequels? Lots of sequels. This is a long series), will be posted on Wednesday mornings (CST) instead of Thursday mornings. Thanks, everyone!!
> 
> Also, I think this counts as the longest chapter of this fic. XD

Sans couldn’t sleep.

This was nothing new. There had been nights over the past few weeks where he had laid in bed all night without even closing his eyes, and other nights when he wasn’t even sure how he got from the front door to his bed, since didn’t remember moving once he reached the house.

He didn’t have dreams anymore. Not the same kind of dreams, anyway. He dreamed if he dozed—though the dreams felt more like replayed memories, hallucinations—but not if he really slept. When he slept, he passed out, dragged down into the depths of nothing until the knocking on his bedroom door shook him awake the next day.

The nights when he slept were better.

Tonight wasn’t going to be one of those nights.

He tried. He really tried. He didn’t want to think about today. He didn’t want to think about tomorrow. He didn’t want to think about his brother’s dust spread all over his clothes, and he didn’t want to think about Papyrus, sleeping in the bedroom down the hall.

But sleep didn’t come.

All he could focus on was the feeling that something was wrong. That vague, biting feeling that crept into his head and clung to him and refused to let go, even if he had no idea how it had gotten there.

Finally, after what felt like an entire night had passed, he opened his eyes and turned his head toward the clock on his nightstand.

2:53.

What time had he gotten in bed again?

He stared at the clock until it hit 3:02, then threw the blankets off of him and climbed out of bed. There was no point just lying there if he wasn’t going to sleep, and if he hadn’t fallen asleep by now, he wasn’t going to.

Besides, that feeling was still gnawing at him from the inside out, and it felt better to move around, like he could run from it, rather than sitting there waiting for it to catch him.

But he had only just put his feet on the floor, not even taken his first step, when his eyes shifted downward, and his mind finally picked up on what should have been obvious from the moment he opened his eyes.

There were no clothes on his floor.

How had he not noticed that when he went to sleep? His floor had been covered in his clothes, dirty and clean, for weeks. It wasn’t like he had been washing them, and every morning, if he hadn’t been sleeping in his clothes in the first place, he just picked up the first shirt and pants he found and put them on.

But there was nothing there now.

He had been gone all day. Had Papyrus come in here and picked up his clothes? He had done that before, but …

Did this Papyrus do that, too? Do his laundry because Sans failed to do it himself?

Was this normal for his version of Sans?

What was his version of Sans even _like_?

Papyrus hadn’t questioned Sans’s … apathetic behavior. His quieter, less enthusiastic tones. Even his dirty, rumpled clothes. Maybe he was still just startled from whatever he thought had happened that had landed them in Hotland, but … it didn’t seem to faze him at all. Like this was what Sans was _supposed_ to act like. Like Sans lazing around and forgetting to do the laundry and sleeping in was normal. Hadn’t he said something about a sentry station? Was that where his Sans worked? Was his Sans even interested in science, had he gone to college, was he different inside or had things just been different around him?

Sans turned his head to the left, toward Papyrus’s room. He couldn’t see him through the wall, of course, nor could he hear him—if he was making any noise, it wasn’t loud enough to pass through. Had he gone to bed? Was he there right now, sleeping in his brother’s room? It should have felt wrong, it _did_ feel wrong, but where else was he going to sleep, it was _his_ room even if it _wasn’t_ his room and he … he …

He needed to get out.

He crossed the room fast enough to ignore how clean the floor was and pushed the door open just slow enough to avoid the creaky hinges. The lights had been dimmed, though there was still a bit of a glow from outside, shining through the windows. He strained his good eye for any movement, any sign that someone was still awake. Nothing. He listened, but he didn’t hear anything either. If Papyrus was still awake, then he was doing a damn good job of staying quiet. But what about …?

Sans’s browbone furrowed, and he took a step out of his room, turning to the left, toward Gaster’s office.

The door was open.

Gaster _never_ left the door to his office open. Except …

He had before, hadn’t he? Before all of this started. There had been nothing to hide, then. Nothing he wanted to keep to himself. No reason for him to hole himself away in a part of the house separate from his sons. Even when they were little, they had always been welcome. If Gaster truly needed to do something they shouldn’t be around, he would be doing it in the lab. The _real_ lab.

If the door was open now …

Sans crept down the hallway and poked his head through the open door.

A desk and a chair and a table full of lab equipment. Papers piled on top of papers, test tubes and supplies.

No Gaster.

Gaster wasn’t back yet.

That shouldn’t have concerned him. For all he knew, Gaster could have been staying at the lab all night for weeks and he wouldn’t have noticed. He had far too many other things keeping his attention. But today, after what had happened, after what Gaster had said he was going to _do_ …

It wasn’t his problem. It _couldn’t_ be his problem, he had _enough_ problems, he couldn’t take this on, too.

But he had already let so many things happen. He had already made so many bad choices. And the latest of which had torn away the person he loved more than anything in the world.

He couldn’t make a choice like that again.

And if he had learned one thing over the past couple of weeks, it was that “doing nothing” was just as much a choice as anything else.

Sans stepped back into his room and closed the door.

It crossed his mind to just go on in the tank top and shorts he was already wearing, but somehow it made him feel too vulnerable, and if he was going to confront Gaster, he would need all the strength he could get. Even if that strength was nothing more than a slight physical reassurance.

Papyrus had taken all the clothes off the floor, so Sans pulled open the drawers of his dresser, searching for anything to wear. The first was empty, and the second. He yanked the third open without much hope for finding anything.

Only to find a blue hoodie tucked away in the corner, still carefully folded, even though all its companions had been taken away long ago.

A blue hoodie.

The hoodie Dr. Japer had given him when he graduated.

He had never worn it. It wasn’t a personal thing—he had loved it, and had every intention of wearing it—but it wasn’t exactly work attire, and he had spent so much time working those first few weeks that he hadn’t even thought of putting it on. After things … changed … he had just grabbed whatever piece of clothing he found first. And the hoodie had he had so adored when he took it out of the carefully-wrapped box had remained in the back of the drawer, untouched.

Dr. Japer.

Was she still worried about him?

Of course she was. She always worried when something was wrong, and she _knew_ something was wrong, she was one of the smartest people he knew, of _course_ she knew something was wrong, and after their last meeting … It was a wonder she hadn’t come barging through the front door demanding to know what the problem was and how she could fix it. Maybe she still would. And then she would see Papyrus and she would _know_ something was wrong because she _knew_ Papyrus and even if that new Papyrus could fool some people he would never fool her.

What would she do then?

He clutched the hoodie tighter in trembling fingers, then slipped it on.

Later.

He wouldn’t be gone long. He just had to see where Gaster had gone. Then … then he could think about that.

Even if he still didn’t know how any solution he thought up was going to help a damn thing.

He started toward his door, but just before he reached for the knob again, he paused, turning around to look at his bed.

Or, more specifically, at what he had hidden _under_ his bed.

It was just about the worst hiding place he could have thought of. He couldn’t technically _see_ it from here, but it was the most obvious place to check. Then again, maybe that made it better. Gaster seemed to think he was too smart for obvious—at least in some respects. Maybe he would think Sans was too smart to hide something important in such an overused place.

He hadn’t been thinking very clearly when he tucked it away after dinner. Besides, it wasn’t like there was anywhere else it would fit.

He didn’t realize he was walking until he was already there, kneeling on the ground and pulling out the container. He hadn’t noticed the faint glow it was giving off, even from under the bed, until he brought it out again, and it shone like the drawings he had seen of the sun. Bright yellow, shining, pulsing.

Alive.

But only as alive as the human had been, lying on that examination table, dead, even if her heard was still beating.

Sans stared down at the last fragment of her soul. The thing they had wanted, the thing they had _needed,_ the very thing that had made her so valuable, the only thing Gaster had apparently seen fit to keep around.

Papyrus hadn’t cared about her soul.

Or at least, no more than he had cared about anyone else’s.

She was just a person to him.

Now she was gone. Now _he_ was gone. All Sans could do was stand there and hold that thing they had all wanted, even just a piece of it, coveted among monster kind as one of the most powerful things anyone could possess …

He paused, clenching his teeth.

He was an idiot.

He was a goddamn _idiot._

But he had already made so many mistakes. So many bad choices. He had already screwed everything up, and no matter what he did now, it wasn’t going to get any better.

He wasn’t quite so stupid as to believe it couldn’t get any worse.

But his hands still moved, still twisted the lid off the container as if on autopilot. The soul glowed a little brighter as he nudged it out into his hand.

It was … warm. Not warm like normal heat, but … he didn’t know. It was foreign. It didn’t _belong_ with him, he could tell that much, even if he wasn’t sure how. It didn’t feel like the S.E., even if that was what it _was,_ that was where the S.E. had _come_ from in first place.

This was a soul.

This was … a human kid. Or what was left of one.

Sans curled his fingers around the yellow glow.

Then, before he could tell himself how bad an idea it was, he brought it against his ribcage and pushed it in.

And the faint heat against his hands vanished.

One. Two. Three.

… Four. Five. Six.

Seven.

Sans waited. He waited for the burning, the pain, he was an _idiot_ but he knew that it would hurt, it always hurt when he got the S.E., so a _soul,_ even a part of one, that would hurt a thousand times worse.

But it didn’t.

It was …

He could feel something. He didn’t know what it was, it was like a … whisper, somewhere in the back of his head. Like someone was talking to him but he couldn’t make out the words, it was too faint to even tell whether or not it was his own voice. It was warm and it was heavy and it was _alive_ but it was so far away.

Sans waited, but nothing changed.

After more than a minute passed, he set the jar back on the ground, slipped out of his room, and walked out the front door.

He didn’t think about where he was going. He just moved. He didn’t think, but he didn’t need to _think_. He knew where Gaster had gone. There was one other possibility—maybe two—but Sans had known his d—Gaster long enough to figure that this was the most likely option.

And when he reached the familiar empty path in Waterfall and saw the thin stream of artificial light pouring out onto the darkened ground, he got his confirmation.

He slowed down from his run as he neared it, suddenly very aware of how much noise his feet made in the mud. His eyes locked on the door, and something odd burned in his chest. It wasn’t like he hadn’t known for most of the day that Gaster had gone into his lab. It wasn’t like there weren’t dozens of more important things going on. It wasn’t even like, a few months ago, he would have _minded_ Gaster going into his lab, even without asking permission first.

But now …

There was nothing left that was really his. Nowhere he felt truly safe. The main lab had been his dream for as long as he could remember, and now he swore he heard screaming every time he walked in the door. As far as he knew, Gaster hadn’t gone in his room yet, but he had little doubt he would—and it wasn’t like Sans had any security measures that would hold up. He couldn’t remember the last time his house had felt like a home.

Even his brother …

His brother …

Sans stepped closer, keeping his footsteps as light as he could. He peered through the crack from five feet away, not daring to get very close to the door for fear of Gaster seeing him through it. But as Sans squinted to make out the tiny bit of movement from inside, he doubted that would be an issue.

The door was barely open—it was a miracle it was open at all—but Sans could still see Gaster’s tall, thin shape hunched in front of the machine, marking something on a clipboard as he adjusted the control panel. He hadn’t changed anything major. Sans couldn’t see any new parts, and nothing obvious had been dismantled.

It had worked, after all.

And he had wanted to …

If he was here now, the only explanation was that he was _going_ to …

He was really going to do it. Now. In the middle of the night. He was going to go to some other universe and take the human souls they had gathered.

Sans clenched his fingers against his sides to keep them from audibly trembling. This was it. If he let this happen, if he just walked away, if he didn’t stop Gaster, he was going to go into some other universe and steal the souls they had gathered. Maybe he would stop with one, or two, just enough to get the seven souls they needed. Maybe it wouldn’t be as bad as all of that. But … even one or two souls would set them back decades. If Gaster was so desperate to get them out here, how desperate would the people in the other universe be?

Would someone else get hurt because some scientist was so intent on getting everyone out that they didn’t care how they did it?

Could Sans follow him? Not without him noticing, for sure. It wasn’t like a ship in there, he had built that machine himself, and at the very most, it could fit four people, and that was only if they were all pressed tight together. There was nowhere for Sans to hide. Not that he would have been able to sneak into the lab itself without being noticed, anyway.

Would Gaster just shoo him off, if he walked in? Tell him it was none of his business? Or would he invite him along, want him to _see_ what he had discovered, as if he was proud of it, because he _was_ proud of it, and maybe he still thought Sans would be proud of it too because he had built it, he had made almost all the modifications, he had done this, he had _built a machine to visit other universes but he didn’t even care._

Sans tried to remember when he would have done almost anything to make Gaster that proud of him.

It hadn’t been that long ago. But it might as well have never happened at all for how distant it felt now.

He took a deep breath, clenched his fists, and stood up a little taller. If he was going to act, he couldn’t put it off. Now or never. Try to stop Gaster or let him ruin someone else’s life, _thousands_ of lives, lives that Sans would never even know.

Sans lifted one foot.

Then the mud squished not five feet behind him, and Sans spun around so fast he almost fell over.

His sockets widened. He blinked. His shoulders fell, even as his soul clenched.

“papyrus?”

Papyrus stared back at him, his eyes almost as wide as he glanced between Sans and the open door in front of him. Sans might not have known this Papyrus for more than a day, but he had seen that expression far too many times on his own brother’s face to mistake it.

“SANS?” he asked, somehow sounding like he was shouting even as he whispered. “WHAT ARE YOU DOING?”

It took a few seconds for Sans’s mind to catch up to what he was seeing. What he was hearing. No. No, he … he couldn’t drag him into this, not again, Papyrus had been dragged into enough, _this_ Papyrus had been dragged into a mess that wasn’t even his, that wasn’t even his _family’s,_ he shouldn’t …

“bro, just … go back home, okay?” he said, holding his hands up as if to motion for his bro—Papyrus to leave. He smiled, even though he knew it wouldn’t come off as reassuring. “i’ll be back soon.”

“WHAT ARE YOU DOING?” Papyrus asked. He had heard him, Sans was almost sure of that, but still he was looking at him with that pained, uncertain stare, taking a step forward and peering over Sans’s shoulder at the door behind him.

Sans shook his head.

“it’s nothing, it’s fine, i’ll be—”

“SANS, PLEASE TELL ME WHAT’S GOING ON,” Papyrus cut him off. Sans went silent. For the first time, in the darkness of night combined with the normal dim glow of Waterfall, he saw the tightness of Papyrus’s expression, his wide sockets, the way the line of his mouth trembled. His gloved hands clutched at the hem of his shirt, his head held high in confidence Sans didn’t believe for a second. “YOU’VE BEEN ACTING STRANGE ALL DAY AND WE BOTH SHOWED UP IN THIS WEIRD HOUSE AND NOTHING SEEMS RIGHT AND NOW YOU’RE RUNNING OFF IN THE MIDDLE OF THE NIGHT AND …”

He trailed off. Sans would have had to be deaf not to hear the tremble in his voice to match the tremble in his bones, the way his words cracked every few seconds, as if it was all he could do not to break down in tears.

“papyrus …” Sans breathed, the tension in his body going limp, his soul heavier than he had thought it could be after all he had been through already.

“You might as well come along.”

Sans jumped so hard he almost fell over, and stumbled twice just turning around to face the entrance to the lab.

He felt like an idiot. He had no doubt he _looked_ like an idiot.

And the way Gaster was staring at him now, standing in the doorway, silhouetted by the light behind him, only made him even more sure.

“Did you really think I wouldn’t hear you coming, Sans?” Gaster asked.

The thudding of Sans’s soul calmed after only a few seconds, and suddenly he felt drained, exhausted by the rush of panicked energy. He swallowed hard and held himself taller, narrowing his eyelights as far as they would go.

“well, you’ve been more oblivious before.”

If Gaster was offended, he gave no sign.

“Yes, I suppose,” he replied, though he didn’t seem to actually be replying to Sans at all. He glanced at Papyrus, just for a second, not long enough for Sans to read his expression. Then he turned around and stepped back into the lab. “Come on. I’m about to get started, and I could use some assistance after I arrive.”

He sounded so casual. As casual as he had sounded while ordering Sans around the lab to find new, more inventive ways of “testing” the human. As if the Papyrus he had looked at wasn’t the wrong Papyrus, as if Sans wasn’t standing there dressed in a hoodie and slippers in the middle of the night in front of the lab that should have been _his_ because Gaster had _given_ it to him.

But it didn’t matter.

Sans didn’t need to ask him to know what he was doing.

Gaster disappeared inside the room, into the area the door covered, and after only a second’s hesitation, Sans began to follow him.

“WHAT ARE YOU DOING?”

Then he stopped.

And turned back around.

Papyrus stood there, staring back at him with wide, concerned eyes. Sans’s chest twisted. He had forgotten, just for a second, that he hadn’t come alone, and suddenly the obvious decision to follow Gaster wasn’t obvious at all. He bit back a heavy sigh.

“papyrus, please, go back home,” he said, holding up his hands in a gesture he hoped was placating. “this is … it’s nothing you need to get involved in, everything’s fine, just—”

“I’M NOT LEAVING, SANS. NOT UNLESS YOU COME WITH ME,” Papyrus cut him off. Sans froze, staring. The concern remained in Papyrus’s eyes, but they hardened—as much as any Papyrus’s eyes ever could—as he pulled himself up as tall as he could be and stared back with more certainty and determination than Sans had seen on his face in weeks. Even if it wasn’t really _his_ face. Papyrus frowned. “I KNOW YOU LIKE TO DO SILLY THINGS LIKE THIS BUT THIS IS TOO SILLY FOR ME TO JUST LEAVE YOU ALONE.”

Sans floundered. He knew that look. Even if it was wrong, even if he had technically never seen it on _this_ face before, he knew that look. And he knew Papyrus wasn’t going to give in.

He would go where Sans went, no matter where that was.

He should just go home. Just take Papyrus home and let Gaster go on with what he was doing. It didn’t matter. Nothing mattered. Whatever happened in those other universes wasn’t his business.

Except …

It _was_ his business.

Papyrus was standing right in front of him, Papyrus was his business, and _Papyrus_ had been yanked out of one of those universes, and he didn’t even know.

He was real. And maybe he wasn’t Sans’s real brother, but he was so much like him, he was a _person,_ just like all the people in those other universes were _people,_ even if Gaster refused to accept it.

He had failed once. He had failed so many goddamn times.

Even if he didn’t know them, even if he had no idea who he would even be failing … he couldn’t let anyone else get hurt because of this mess.

And if he couldn’t force Papyrus to stay behind, then he would just have to make sure he was safe wherever they went.

He gave a small nod, even though he knew it was pointless. It was never about him giving Papyrus permission to come along. Papyrus went where he wanted, whether Sans liked it or not.

And just as expected, as soon as he turned and started into the lab, he heard Papyrus’s footsteps following only a few steps behind him.

Gaster was already standing in front of the machine, checking it over, and gave them only a glance as they stepped into the room and pulled the door shut. After what must have been less than a minute, he nodded to himself, set the clipboard aside, and pulled off his lab coat. It was, from what Sans could remember, the first time in more than a month that he had seen him without it.

How many years had it been locked up in the closet before Sans pulled it out?

How had Sans ever thought that seeing him in it was a good thing?

Part of Sans, somewhere deep down, had hoped that when the lab coat came off, so would … this. All of this, _any_ of this. But it didn’t. Underneath the lab coat was one of the same outfits Sans had seen his dad in a dozen times, turtleneck sweater with black pants and a jacket, but it didn’t look like him. Now, Sans wasn’t sure if there was anything in the world that could make him look like himself.

He was dressed nicely—nicer than just his usual turtleneck. Wasn’t that the same jacket he had worn to Sans’s college graduation? He couldn’t remember. That hadn’t even been that along ago, maybe six months, but he couldn’t _remember._ And he didn’t care. Or … he did, but he didn’t, and nothing mattered but _everything_ did at the same time. Then Gaster was moving, picking up the clipboard and another device Sans didn’t recognize, before pulling open the door to the inside of the machine and stepping in. Sans forced his feet to move before they could resist him, Papyrus shuffling behind him, nervous, more nervous than such an innocent version of his brother should have ever been, but unhesitating nonetheless.

It was cramped, just as Sans had known it would be. Gaster and Papyrus both had to hunch over a bit to keep from bumping their heads on the ceiling, and Sans was closer to Gaster than he had willingly stood in weeks. Sans scooted as close to his brother as he could get, and Papyrus pressed closer still.

It felt weird to touch him now, now that he knew, now that every fleeting moment of contact reminded him that this wasn’t his brother, not really, not _ever._ It felt weirder to notice that the texture of their bones was the same. The same neutral temperature. The slight, nervous, uncertain tremble he couldn’t quite hide.

Gaster pulled the door shut, turning the handle to lock it in place, and Sans’s vision went almost completely dark. He had never thought to install a window in the door to let in light or even allow him to peek outside to see where he had arrived before he stepped out. He had never gotten that far. He had been far too focused on just _getting_ where he wanted to go to consider needing to check his surroundings once he got there.

Besides, if he was only going back in time a few months, maybe a year at most, it wasn’t like there would be anything to watch out for.

The control panel near the inside of the door flickered on, allowing him a glimpse at Gaster’s face as he typed something in Sans couldn’t quite make out. He glanced at his clipboard once or twice, pausing to mark something down on it before he continued tapping on the keys.

“do you actually know where we’re going?” Sans asked, and the sarcasm he had tried to force into his voice came out sounding far more like anxiety.

Gaster offered him a brief, blank glance before returning to the keypad.

“No.”

After all Sans had been through, everything he had lost, that shouldn’t have made a shiver run through his bones. But it did. A few seconds later, he felt bony, gloved fingers wrap around his own, and it took him less than a second to squeeze them back just as tight.

He tried not to notice how hard they were shaking.

Gaster pressed another button, and the machine began to whir.

It wasn’t like Sans had imagined, not that he had spent much time imagining it recently. The sci-fi novels he had devoured as a kid had made him imagine traveling through a vortex, the machine bumping against objects that really couldn’t be there because it wasn’t like there was a physical _time-stream,_ but even if it was unrealistic it was still fun. But this wasn’t time travel. They were traveling through _dimensions._ What did that even mean? Were they physically traveling? Not physically in the normal sense, it wasn’t like a car, it didn’t _feel_ like a car, it felt like they were standing still yet moving at a million miles an hour.

The hand in his squeezed tighter, and Sans clutched it so hard he swore he was going to crack the bones underneath.

It might have been a minute, it might have been an hour, it might have been a day. Time had been a blur to Sans for a long time now, and standing in the dark with nothing but his brother’s hand to ground him with a machine traveling places he had never dreamed a machine could take _anyone_ didn’t help things. He clutched Papyrus’s hand until his own fingers hurt, and Papyrus kept squeezing back, and the pain was the most welcome feeling in the world.

The lights blinked, the machine hummed and buzzed, the world blurred and twisted and Sans couldn’t move even though he wanted nothing more than to get far, far away.

Then they stopped.

Or … whatever counted as stopping, if they had never really been moving in the first place.

The machine began to quiet, the whir dying down, but only once it had gone completely silent, and stayed that way for a good ten seconds, did Gaster reach to open the door. Sans could feel Papyrus’s hand shaking in his, so hard now that he couldn’t tell whether or not his own hand was shaking in return.

Sans squinted when the light flooded into the darkened space. Dim light. Not quite like the light from the lab, but … similar. Weirdly similar. Gaster was stepping out the door already, his feet were touching something solid, tapping, just like they tapped on the hard lab floor. Sans didn’t want to leave the machine, he didn’t want to go out there, he didn’t want to see this, but he felt Papyrus’s hand in his own and it wasn’t much but it was _enough_.

He stepped out the door, Papyrus at his side.

Gaster was already at the other door—other door? The door to the lab, but this _wasn’t_ the lab, they had left the lab behind, this was another world, so there should be … whatever there would normally be in this place, was there a lab in this universe, too, but it looked the same but _not_ the same and he was walking even as his head rushed to keep up with what was going on and Gaster was pushing the door open with so little caution it made Sans want to shake him but he kept following him anyway.

The door was open.

And even with his eyes still adjusting to the change in light, Sans could see.

As hard as he had clung to it before, Papyrus’s hand fell from his grasp almost without notice.

It was … Waterfall.

Waterfall late at night, just like they had left it.

Sans furrowed his browbone.

His first thought was that it hadn’t worked. Of course it hadn’t. They were still here. But …

He turned to his left, toward Gaster, who was already stepping out further and looking around at the environment nearby. He didn’t seem disappointed or irritated. Just … interested. He held his clipboard, the unnamed device tucked against the elbow of his arm, but didn’t move to pick up his pen, focusing instead on everything that surrounded him, as if it _didn’t_ look exactly the same as the place they had just left.

After a few seconds, Sans let himself look to the right. Yes. It was Waterfall. Exactly the same as it had been when he left it. What was that, five minutes ago? And it hadn’t changed. Yes, it was the same, it was all just the same, Gaster had been lying or the machine hadn’t worked and …

He looked over his shoulder, back into the lab.

But it wasn’t the lab.

It was darker, sure, he had noticed that before, but … there had been other things there. He didn’t know what, he hadn’t paid much attention lately, but he _knew_ something was different about it. It was emptier. It was the same lab he had left behind, but it _wasn’t._

He was tired. He could be imagining it.

What he wouldn’t have given to believe he was imagining it.

“WHERE IS HE GOING?”

Sans jumped. His eyes drifted up to Papyrus, his brother, _the wrong version of his brother if there weren’t any other universes than how was he here because he was dead dust gone forever_ —standing just to his left, staring out at Gaster’s quickly-shrinking form. He had looked upset before, _scared_ before, and it had only gotten worse. Of course it had. What about this would have calmed him?

He spent several seconds trying to think of anything to say to comfort him, a half-truth, a flat-out lie, he didn’t care, as long as it made Papyrus feel a little bit safer. But there was nothing. So finally he let out a long breath and shook his head.

“come on, bro. we’d better follow him.”

“WHAT DID THAT MACHINE DO?” Papyrus asked. There was an odd tinge to his voice now, and it took a few seconds for Sans to recognize it as fear. _Real_ fear, not just anxiousness or uncertainty. Papyrus was afraid. And if he was acting afraid, if this Papyrus that had been so bright and happy looked _genuinely afraid,_ then that meant he was terrified. “WHY ARE WE GOING BACK OUTSIDE?”

Sans gritted his teeth so hard he started to wonder if he really could pull them apart. He looked at Gaster, growing smaller by the second, then back at Papyrus, before jerking his head away again.

“you can stay here, if you want. you should …”

He trailed off, his mouth curling into the closest thing to a frown he was physically capable of.

Should he? If this really wasn’t their universe …was the lab still safe? Glancing behind him, he confirmed, yet again, that it didn’t really _look_ like the lab. There was … something missing. Several somethings missing, though his head wasn’t working well enough to tell him exactly what.

This wasn’t his lab.

And even if it was …

It wasn’t like the lab had been safe for a long time.

Papyrus wasn’t safe in the lab, and he wasn’t safe with him.

But at least if they were together, Sans would be able to step in before something went wrong.

He had left his brother alone before and seen the consequences. He wasn’t going to let that happen again.

And just as he started to take back his suggestion, Papyrus stood up taller and shook his head.

“I WANT TO STAY WITH YOU.”

And all Sans could do was close his eyes and nod as he started toward Gaster, Papyrus close at his heels.

It took him a minute to catch up. Gaster wasn’t running, but he wasn’t walking slowly—at least, not as slowly as Sans would have expected of someone visiting a parallel universe for the first time. If it had been Sans leading this adventure, he would have been looking around, taking in all the sights, and probably wondering, at least a little, if he risked messing something up by being here.

But Gaster had already proven he wasn’t worried about that, hadn’t he?

Sans fell in at his side, and heard Papyrus stop a few steps behind them, as if he wasn’t sure how close he wanted to get. Sans wasn’t sure whether to feel relieved or hurt. Because that was what had happened so many times, Papyrus left behind while Sans and his dad walked ahead, doing their own thing, leaving Papyrus to take care of the house, hold down the fort, make them dinner when they come home and pretend that was all he ever wanted in life—

Gaster was talking.

Murmuring, more like it. Muttering under his breath, like he used to do in the lab when he was in the middle of work. Sans turned to face him, only to find him still staring at the clipboard, taking out the device to press a few buttons, stare at the display screen, then tuck it back against his arm and write something down.

“—ber one, normal ambient sounds typical of Waterfall, no monster life encountered as of yet, continuing to—”

“what are you doing?” Sans snapped before he could think of anything else to say—or decide to stay silent.

Gaster spared him a glance, not even long enough to read his expression, before he returned to the clipboard.

“Noting my observations. I would think you’d be well acquainted with the scientific process, Sans.”

Sans raised one half of his browbone. “didn’t you make any ‘observations’ before?”

There was a flinch. A brief, almost imperceptible flinch that in any other situation, Sans might have found satisfying.

“I was distracted,” Gaster muttered, without turning his head.

Sans was close, so close, to commenting on that. But then he looked to his left and saw Papyrus strolling along, just a few feet away from him. He stayed silent. Finally, his irritation, his bubbling unpleasant emotions, began to fade, and he found his eyes wandering again, taking in the details of their surroundings that Gaster seemed to think of as only important to mark down in his notes.

He wasn’t sure what he had been imagining when he thought of parallel universes before. He must have known that they wouldn’t be all that different from the one he lived in himself, but this was … he had a hard time believing that this was really another world. It looked so much like the one they had come from. It looked _just_ like the one they had come from.

But something felt … wrong.

It wasn’t a strong feeling. He probably would have ignored it if not for everything else, if not for the fact that they _had_ stepped in that machine and Gaster had no reason to pretend that this was working if it wasn’t.

If not for the dust he could still feel on his T-shirt, and the squishing of his brother’s footsteps walking at his side.

“Did we have to come out here so _early_ , though?”

Sans stopped only a second before Gaster did, and Sans could feel Papyrus stumble to avoid crashing into them both. Without a word, they all took several steps back, out of sight, behind the wall they had just passed, away from the faintly whining voice in the distance, accompanied by two sets of footsteps.

There was a chuckle. Older, masculine. Oddly familiar.

“I told you, LeeLee, the stones only do this if it’s been quiet for a while. We might have to wait an hour or two after we arrive for them to react properly again—“

“An _hour or two_?”

“Didn’t I tell you all this yesterday?” the man’s voice laughed.

The other voice huffed, just as two people came into view, far enough away not to notice the three people hiding in their peripheral view.

“No, you didn’t,” the first voice went on, irritated, almost mocking. “You said, ‘LeeLee, I have a very important assignment for you, meet me at the Hotland bridge tonight at 3:30,’ then you ran off to get snacks before I could say anything about it.”

The man looked at his companion, walking to his right, and finally, Sans got a glimpse of the face that matched up with the voice in his head.

Dr. Frewth.

That was Dr. Frewth.

The same smooth pink skin, the same goofy T-shirt under his lab coat, the same wide smile he shared with everyone, no matter how well he knew them. It was _him._

But … that odd feeling hadn’t gone away.

They weren’t home. Sans knew that, as well as he knew what it felt like to breathe. They weren’t home. But that was Dr. Frewth, strolling along with a young monster—was that who his intern was in this universe? What had happened to Bettie?—completely ignorant of Sans watching him from less than ten yards away.

“Oh,” he answered at last, his smile falling in something almost sheepish before he cleared his throat and smiled again. “In that case, I don’t suppose treating you for coffee would make up for it?”

The blue-skinned monster at his side pouted, but looked almost swayed. “… I’ll think about it.”

Dr. Frewth chuckled, and both of them walked on, down the path, out of sight, leaving Sans staring after them and fighting back every instinct he had to follow.

It wasn’t them.

It really wasn’t them.

Just like Papyrus.

It was them but it wasn’t the _same_ them and … and …

“Sans. Come along.”

Sans jerked his head to face Gaster, starting ahead without even looking at him. Papyrus glanced back and forth between the two of them, lingering on Sans, confused, nervous, and lost.

He didn’t seem the least bit interested in Dr. Frewth. Like he didn’t even know him.

Maybe his brother had never spent much time around Dr. Frewth, but he definitely _knew_ him, and if this Papyrus _didn’t_ …

“SANS?” Papyrus asked.

Sans swallowed back the ache in his throat, the words that tried to force their way out, and let out a long, shaking breath.

Then he followed Gaster, Papyrus trailing along behind him just as he had before.

Just as he had for so many years, constant and loyal and sure.

They kept walking, Gaster muttering to himself and jotting down notes, but otherwise silent. They didn’t run into Dr. Frewth again, or anyone else. Sans wondered if they were going to the Wishing Room. Wasn’t there a path around there that led to it? He couldn’t remember. Maybe it was different in this universe anyway.

He stopped glancing at Papyrus after the first few minutes. It wasn’t like there was anything to say, and if Papyrus wanted to talk, he probably would have spoken by now.

Or at least … _his_ Papyrus would have. This one seemed just as chatty, even more so, but maybe …

Sans let his attention drift back to this other version of Waterfall, identical in almost every way. He tried to pick out anything that could identify this world as another, anything that would make it clear except for that other Dr. Frewth and LeeLee, who the _hell_ was LeeLee anyway, but everything was the same, and that was the worst part, it would have been easier if everything was suddenly bright orange and polka-dot but it was the same Waterfall, the same place he had walked through a thousand times, even though he knew now it was anything but.

He was so focused on his surroundings that he didn’t notice Gaster turning around until he had already passed them.

He blinked, pausing before spinning around, catching sight of Papyrus doing the same out of the corner of his eye. Gaster paid them no mind, walking back the way they had come, scribbling something else down on his clipboard before tucking it against his side.

“what?” Sans asked, even as he scrambled to keep up, Papyrus close at his heels. “we’re leaving?”

“Yes,” Gaster replied, without even a glance in his direction.

Sans furrowed his browbone. “i thought you wanted to get the souls.”

That earned him a glance, just a glance, not even a second long. Gaster’s pace didn’t falter.

“I do. But I rather doubt that the king will just hand them over if I ask him, or that they are kept in an easy-to-access area. And I’m not planning to start a fight unless it becomes necessary.”

For a second, and no longer, Sans tried to figure out what exactly Gaster would consider “necessary” before he outright attacked the king.

Not their king. _This_ king.

The king he somehow brushed aside as not important, just like everyone in all these other worlds, even when he had come to some place like this to find a replacement for his dead son.

For two seconds, he wondered, if Gaster did start a fight, whether he would have any chance of winning.

“so what?” he asked, before he could follow that train of thought any further. “what are you gonna do?”

He listened to Papyrus’s footsteps behind him, the uneven gait Sans had long learned to associate with anxiety. He wanted more than anything to turn around and offer some reassurance, but he had a feeling anything that came out of his mouth right now would only make things worse.

Gaster slowed, then walked a little faster, forcing Sans to struggle on his much-shorter legs to keep up.

“There are other universes,” he replied. “Many other universes different enough from ours that the souls may be unguarded. If possible, I’d like to find one of those and take the souls peacefully. If that isn’t possible … I’ll have a list of all the universes we can return to.”

He glanced down at the clipboard at his side, clutching it a little tighter. Sans swore there was something like pain, something like regret, on his face. But it was gone before he could be sure.

None of them said a word the entire way back to the room.

It wasn’t quite so overwhelming, riding in the machine the second time, though it was still far from pleasant. Papyrus still grabbed his hand as soon as the door shut, and Sans still clung to it, unsure whether he was being comforted or doing the comforting or a little of both.

He knew it wasn’t his brother. He had known that before they came here, and he was even more sure of it now.

It still felt better holding his hand.

The next universe, when they first stepped out into it, looked the same. Almost exactly the same. A bit of time had passed, and it was a bit later, but it was still the middle of the night, with virtually everyone still in bed, and no sign of any significant changes that would mean Gaster would be able to find the souls more easily. Maybe something important was different. Maybe it actually was identical. Either way, Gaster spent no more than ten minutes there before he started back toward the lab with a disappointed frown on his face.

The next universe was the same. And the one after that. Each time, Gaster wandered around, taking in their surroundings. He stayed a little longer in the third one, as if he had caught something interesting or unusual, though he didn’t say what it was. Based on the irritation that showed on his face once they reached Hotland, and how quickly he turned around, nothing had come of it. By the time they left the fourth universe, several monsters had started to come out of their houses, ready to start their days. It was still early, and it would be a while before the full hustle and bustle began, but it was harder to get around without being noticed. Though Sans didn’t have time to double-check, he swore he saw another few familiar faces on their way back.

Maybe there had been changes before that. Changes other than Dr. Frewth having a new intern, other than the exact people who came out early in the morning to start their jobs. But it wasn’t until the fifth universe that the changes became too stark to ignore.

They stepped out of the door just like they had in the previous four universes. Sans waited until Papyrus had slipped past him before pushing the door shut, out of reflex more than any desire to keep wandering eyes away from the machine. But just as he was about to walk forward, as he had every time before, he turned and found both Gaster and Papyrus standing completely still, their eyes locked off in the distance.

Gaster had commented on the “ambient noises of Waterfall” during their first stop. Until now, Sans had brushed it off as another quirk. It was just Waterfall, even if it was in another universe. Sans could understand trying to make notes about everything, even the things that seemed obvious, but Waterfall was Waterfall, no matter how the universes changed.

He had never noticed the faint squishing of mud in the distance. The chirping and buzzing of insects. The splashing of water, more than just the trickling that never stopped. The hum of life all around them, the same hum he had heard every time he visited, every time he went to his lab, even when it was late. The hum he had never noticed, because it had always been there.

The hum that had completely disappeared.

It was … silent. Aside from the trickle of water, there was … nothing. Had there ever been _nothing_ in Waterfall, in _any_ part of the Underground? Sure, there were places where less people lived, and Waterfall wasn’t half as crowded as the capital, but there wasn’t exactly much wide open space down here. Not unless every single monster had decided to crowd into one spot at exactly the same time.

But …

It had felt wrong before, but that had been more of a vague sense of uneasiness. This was … _wrong._ He couldn’t even put a name to it.

And why was it so damn _quiet_?

Gaster started forward, and Sans followed, almost without thinking. A minute later, he glanced to Papyrus and found him looking from side to side, his browbone furrowed, his mouth pressed into a tight, confused line.

“WHERE IS EVERYONE?” he asked, but even though he spoke more quietly than usual, it still made Sans flinch. “AREN’T THERE USUALLY MORE PEOPLE AROUND HERE?”

Sans looked around. They had gotten a bit further away from the lab by now. And there was no one. Not a single person. Not a single sound. Just their own breath, and their own feet squishing in the mud.

He looked down.

And he froze.

The mud in Waterfall was brown. The mud _everywhere_ he had ever seen was brown. Maybe there was mud somewhere else that wasn’t brown, but he knew this mud, and it was supposed to be brown.

But _this_ mud was speckled with white.

White dust.

Sprinkled over the mud like powdered sugar.

“SANS?”

Sans jerked his head back up and started walking again before Papyrus could come to a full stop. Before he could follow Sans’s gaze and see what he had seen. Before he could figure out what it was.

Had Papyrus ever seen monster dust before?

He hadn’t thought anything about it when he saw it on Sans’s shirt. He had thought it was … he had thought it really _was_ powdered sugar, he had touched it like it was nothing, _he had touched his own dust and he didn’t even know and_ —

“it’s … it’s nothing, bro, i’m fine,” he stammered out, his voice breathy and shaky no matter how hard he tried to steady it.

Papyrus just looked at him. He had that same expression as before, the expression that made it so, _so_ hard for him to remember that this wasn’t his Papyrus, that they weren’t the same, they had lived completely different lives, but _god, no one but his brother had ever looked at him like that._

Sans turned away, and Papyrus didn’t say anything else.

He kept moving without a word, his eyes locked on the ground ahead of him. The dust kept going. It wasn’t constant, not like it had been intentionally spread. It looked like it had been … walked on. Spread around unintentionally through getting caught on someone’s shoes and trekked about. Sans felt something like nausea crawling through his bones even though he knew there was no way he could actually throw up. He wished he could. Maybe it would have been a good distraction.

After several minutes of silence, he looked ahead, toward the figure trailing just a few yards ahead of them, and finally noticed that Gaster wasn’t taking notes.

Not muttering to himself. Not scratching anything down on his clipboard.

He hadn’t even stated an entry number.

He was just … walking.

Slow and rhythmic, as if he didn’t realize he was moving at all.

And suddenly it was real. Everything he saw around him, everything he could hardly _believe_ he was seeing, it was all _real._ All that dust, scattered in patches all over the ground, that had been _people._ Not just one or two people, the further they walked the more he could see it, it had been dozens, maybe even _hundreds_ of different people.

Dead.

Murdered.

Left as piles of forgotten dust, none of them even given a proper burial.

Someone had done this.

Someone had killed them.

Someone had …

Sans swallowed the nausea growing in his throat, his teeth gritted, his body tense and shaking.

“what happened?”

The question came out without his consent, but he didn’t regret it. He turned to look at Gaster, waiting for a response, but Gaster just kept staring in front of them, his face blink, his eyes cold and hard. He didn’t even look upset. He just looked … tired. Like an old, old man who had seen this before, like an old, old man who wasn’t _surprised_ to see it again.

Sans glanced over his shoulder, toward where Papyrus trailed behind them, lost and confused and unsure, but trying to keep his head high. For a second, Sans considered moving back to his side, taking his hand, even pulling him into a hug, anything to soothe the swirling emotions on his face. But then his hands curled into fists, and he turned to Gaster again.

“what happened here?” he repeated, keeping his voice quiet, even though, in the silence, he had little doubt Papyrus could hear them. Gaster’s eyes flicked in his direction, not even for a full second, but long enough for Sans to see. His own eyelights narrowed. “you know, don’t you?”

Gaster didn’t look at him again, and for a good half minute, Sans just stared at him, his feet moving on reflex, his eyes wide in expectation.

Then Gaster’s eyes lowered, just a bit, to focus on the muddied ground below them, coated in dust.

“A human happened.”

Sans blinked. Gaster flicked his eyes to him again, something like irritation in his gaze, though it was dull and he didn’t seem to have the energy to be properly annoyed. He let out a soft breath.

“You know just as much about this as I do, Sans, and you’re smart enough to put the pieces together,” he went on. Sans could hear the faint squishing of Papyrus’s footsteps nearby, unsteady. He was listening. Sans couldn’t bring himself to look at him. If Gaster noticed, he gave no sign, simply staring ahead with the same blank eyes. “If a human is capable of creating a new universe where they’re still alive, if they can come back to a new universe every time they do so, do you not think that eventually there would come a time when they would never die? When they would find a way to escape everyone who tried to stop them?”

He didn’t shift his gaze, but Sans could feel his own eyes scanning the ground around them again, more thoroughly. If he looked closely, he could see footprints in the mud near the piles of dust. Small footprints, small shoes on small feet.

“When they would do what humans do best?”

Sans felt a tremor go through each of his bones, culminating in his skull and short-circuiting his mind for a few seconds before he forced the sensation away.

“there are other universes like this,” he murmured, glancing back again to make sure Papyrus couldn’t hear him, even though he was sure that if Papyrus wanted to listen, he would hear whatever he pleased.

He looked back to Gaster, just in time to see him close his eyes and let out a sigh.

“The machine keeps track of the numerical indicator of every universe it visits. Those indicators don’t mean anything to us, they’re just random numbers generated in the machine’s attempt to assign a geographical location when there _is_ no geographical location, at least not one that varies.”

He opened his eyes, and even with only half of his face visible, Sans could still see the raw pain that flashed across his face.

“As far as I can remember of the numbers, I haven’t been to this one.”

Then the pain was gone, as was the brief reminder of what his reaction might once have been to a tragedy like this, had he come across it six months ago rather than now. Or maybe he wouldn’t have reacted like that. If Gaster had proven anything over the past few months, it was that just because he had given off one impression over the past nineteen years, that didn’t mean it was always accurate.

“and you saw this happen,” he said.

Gaster’s mouth somehow pressed even tighter than before.

“I saw the results,” he replied. His eyes flicked to Sans again, and Sans couldn’t tell whether he looked more tired or irritated by him not catching on more quickly. “This is what humans do, Sans. You’ve already seen what they’re capable of.”

Sans tried to speak, but the words died in his throat before they had even begun to form.

No. She had … they had … it had been _his_ fault. Gaster’s fault. The human wouldn’t have ki—hurt—it wouldn’t have happened if Gaster hadn’t put her there in the first place. He had hurt her, terrified her, traumatized her, _tortured_ her, and then Papyrus had tried to help her and she had misunderstood and fought back. That was all there was to it. She had been fine before Gaster had gotten ahold of her. Papyrus had trusted her, he had _believed_ in her. Surely she …

But she had still done it, hadn’t she? She had still murdered him, when he was only trying to help. She had grabbed a knife and stabbed him, over and over, she didn’t need to do it that many times, once would have been plenty, even if he _had_ been attacking her, but she just kept doing it, he could hear her even before he opened the door, just like he could still see Papyrus’s limp body clattering to the floor and—

It had been Gaster’s fault. Hadn’t it?

Or had it been inevitable? If Sans hadn’t turned her in, if she had stayed hidden in Papyrus’s room, if by some miracle Gaster hadn’t found her …

Sans looked around one more time at the piles of dust surrounding them.

Would the human have still attacked, if Gaster hadn’t hurt it first?

Was that just what humans did?

Would she have kept going, that desperate to get out of here? _Had_ she kept going, in some other universe where Sans hadn’t killed her, where she had escaped? Would she have killed every monster in her sight just because that was what her species _did,_ would she have left them all in piles of dust, would she have slaughtered everyone just so she could get through the barrier?

This human had.

He didn’t even know if it had been recent. Maybe it _had_ been that kid. Or maybe it had been another kid, decades ago, nearly a _century_ ago now.

He wasn’t sure he wanted to know.

“let’s go.”

His voice came out as barely more than a croak. He sounded like a kid, a kid whose voice was breaking with fear he didn’t realize he had been feeling until now. But at the same time, it was a voice that left no room for argument.

Gaster didn’t stop. Sans glanced at Papyrus, made out the creases in his facial bones, the way he clutched at his arms and shifted his weight from foot to foot. Sans curled his hands into fists and turned ahead again.

“gaster. let’s go,” he repeated, louder, more confidently than before. He swallowed. “you’re not gonna learn anything here. let’s just … let’s just go back to the machine and try somewhere else.”

Sans expected him to protest. After all, a universe where the human souls weren’t guarded … he could search for them at his leisure, if the king had been killed, too, then he could stay here as long as he wanted and find the human souls and take them all back with them. Maybe there weren’t any souls, maybe this had happened too quickly for the king to start gathering them, but there was a good chance for there to be at least _one._ And Sans knew that. He knew that the most logical decision was to stay here. And wasn’t that what Gaster had been claiming to do over the past few months? The most _logical_ thing? The _best thing for them_?

It would have made total sense for Gaster to ignore him, to brush him off, to speed up, even, to get to the castle faster.

Which was why Sans took a second to realize his dad had stopped.

He didn’t say anything. He didn’t move. He didn’t meet Sans’s eyes. He just stood there as Sans stumbled to a stop and Papyrus stopped beside him, and Sans stared, waiting for the dismissal, waiting for him to start walking again so Sans could chase after him and try to convince him this was a bad idea or, better yet, just run back to the machine and leave him in this godforsaken place.

Then, before Sans could think, Gaster turned around and walked past him, back toward the machine.

Sans stood there, legs refusing to move, for a good ten seconds before he forced himself to take a step. Then another, and another. Out of here. He was getting _out_ of here. Him and his brother, anywhere but here would be fine, he just wanted to get the hell away from all this dust, how many people had died here, how many people they _knew_ , he couldn’t even imagine it but at the same time he swore he could hear their screams echoing in his head.

And even though he was facing away from him, all Sans needed to do was look at the tension in Gaster’s back to know that it got to him just as much.

Maybe that should have been a relief, that there was still something in him that _could_ feel disturbed at a sight like this. But all it did was make the man in front of him blur into two, before and after, so different yet so incredibly alike.

This was the man he had grown up with.

This was the man who had told him he loved him.

This was the man he had loved more than anything in the world.

And he was the same man who had ruined his life.

“HE’S NOT FROM THE SENTRY STATION, IS HE?”

Sans’s head jerked up and to the side. He had already known Papyrus was looking at him—he could hear both their footsteps, nervous, uneven, side by side, where else would he be?—but it still made him tense.

He swallowed, grit his teeth, and looked away.

“… no.”

He didn’t say anything else, and though he waited several minutes for Papyrus to ask him anything else, he never did. They just kept on walking, following the only other living monster back through the dust-strewn Waterfall toward the machine.


	45. Chapter 37

**Notes for the Chapter:**

> Just a quick note to confirm something: I _adore_ Papyrus, and think of him as very talented, unique, and someone who understands much more than people give him credit for. This story is ... almost entirely in Sans's point of view for a reason. This is Sans's story, primarily, and it's establishing where he is at this point in his life - and how he views and treats his brother. But though Sans still technically takes the lead in this whole series, Papyrus is going to play a much, much bigger role in future stories, and will be growing and changing a lot as a character in the sequels (as well as other people seeing more than what he currently presents to the world).
> 
> There's a lot going on in his head now, he just isn't expressing it ...
> 
> So if you're one who loves a complex!Papyrus, stay tuned. Things are going to get a lot deeper in the future ...

Sans would have lost track of the universes they had visited if not for Gaster counting them out each time they arrived.

They were rarely there for very long. Just long enough for them to leave the room and for Gaster to make whatever notes he needed about the universe without being noticed. As the day wore on, that grew harder and harder. While they may have switched universes with every jump, they stayed at the same point in time, which meant that they had to avoid more and more people who were going to work or going about their day.

Occasionally, people saw them. Even more occasionally, they got a second glance, a strange look.

Once—just once—Sans swore that a woman was about to speak to them, to call out to them, but they were gone before she had the chance to speak.

Sometimes the worlds were full of life, like the first universe, like their own. Other times … there was dust. A little. Or a lot.

The dust had become so ordinary that when Sans stepped out of the lab and heard nothing but the faint trickling of Waterfall, it took him a minute to notice that he saw no white powder on the ground.

It took him another minute after that to notice that Gaster wasn’t muttering to himself.

He wasn’t even looking at his clipboard.

He was just walking, staring ahead with a face Sans wished he knew well enough to read.

And in the silence, Sans finally took the chance to look around for real.

It was empty, just as he had thought. Silent. Dead. But there was no _sign_ of death, none that he recognized anyway. There wasn’t even the lingering feeling of heaviness, danger and grief that had weighed down previous universes, even those where some people were still alive.

There was no dust. It was Waterfall, just as he remembered it.

Just … without the people.

“WHERE IS EVERYONE?” Papyrus asked, as if sensing that no one else was going to say it out loud. “DID THEY ALL MOVE?”

Gaster didn’t say anything, and though Sans tried to think of a good response, he came up blank.

No dust was a good sign, right? If everyone was … there would have been dust. There would have been a _lot_ of dust, or at least enough for him to see it. But there was nothing. And as they walked further, there were no abandoned items on the ground either, no clothes, no toys, no shopping bags dropped in a panicked frenzy. Everyone was gone, but … they hadn’t left in a hurry.

None of them said anything as they walked through the rest of Hotland, past the Core and into the Capital. And no one showed up. The further they got, the more Papyrus looked to be spot-on. Everyone _had_ moved. There were still some things left behind, but all the shops had been properly closed up, the houses cleared out. Maybe a little rushed, a few things left scattered here and there, but for the most part, it looked a bit like Sans suspected the Ruins had once everyone had moved on.

Except … where else was there to move on _to_?

He knew, of course. Gaster had said it was a possibility. Sans had _known_ it was a possibility.

But that didn’t make it any easier to accept it.

They walked through the castle, just as empty as everywhere else. Their footsteps echoed around the empty rooms, their breaths as loud as strong gusts of wind. Sans found himself glancing back at Papyrus every few seconds, as if to assure himself that he wasn’t alone. Nowhere in the underground had ever felt so empty.

But Gaster didn’t react.

At least, not until they reached the throne room, and found a garden of flowers.

Withered. Some of them still sprouting through, but most of them dead.

Sans had only seen the castle a couple of times, when his whole family had gone to visit the king. It wasn’t a regular excursion, but it wasn’t like the king was inaccessible. And he had always loved kids. Sans could still remember playing in the throne room when he was little, maybe eight or nine, he could remember the king handing him his own watering can and showing him how to tell where to water and where the flowers were already satisfied.

The king loved his flowers.

And they were dead.

Not just in the throne room, but in the garden, too. Just … dead. Abandoned. They had only ever stayed alive inside due to the king’s careful attention, and now they were …

But there was no dust. No sign that a human had killed everyone. So why …?

The truth nipped at the edges of his mind, but still he resisted.

He moved faster now, and Gaster didn’t protest, walking even faster at his side while Papyrus stumbled behind him, confused but determined to keep up. He could barely remember what turns to take, but Gaster could, and Sans found himself following him through the short span of hallway remaining to reach the barrier.

Or, rather, where the barrier had been before.

But the barrier was gone.

Sans started to say something, started to ask something, but there was nothing to ask. It was right in front of him, or, rather, it _wasn’t_ right in front of him. The same barrier that had trapped them all down here for two thousand years, the barrier that had made his dad so obsessed, the barrier that had _ruined his whole life_ —

It was gone.

And behind it …

“ARE WE GOING OUT THERE?” Papyrus asked, snapping Sans’s attention back to him. He was smiling, his eyes wide and eager, his feet already twitching as if to step forward. “IT LOOKS NICE OUT THERE. I’VE NEVER SEEN ANYTHING LIKE THAT BEFORE! COME ON, SANS, LET’S GO!”

Sans held out a hand. “wait, papyr—”

But Papyrus was already walking out.

Out.

Onto the surface.

It was … hard to see much from where he stood now. It looked a little like they were under the cover of a cave. Hadn’t the surface been brighter than that, though? Even through the barrier? It looked … dull. Gray. Was this surface different from the surface in his universe? He had never seen any changes that major, changes that couldn’t have been caused by one of the human kids, but then again, he had never approached the barrier in any of the other universes.

The barrier had never been _broken_ in any of the other universes.

Gaster followed Papyrus with slow, but determined steps, and though Sans spared him only a glance, he swore his hands were shaking.

Two thousand years.

Two thousand years, and the barrier was gone.

And for a second, Sans remembered just how badly he had wanted that.

Everything he had been willing to give up for it.

Then he remembered everything he _had_ given up for it. Given up in vain, because their barrier _hadn’t_ broken, they were still trapped, trapped and everything he knew and loved was gone and …

Gaster and Papyrus were already stepping out of the cover of the cave, and without thinking, Sans followed.

There was a noise he hadn’t noticed before. It sounded like … like the shower when it was running, only bigger, like there was a shower everywhere, and now that he looked closer, he could see what seemed to be drops of water hitting the ground—the _real_ ground, with mud and grass and plants and god, it was real, it was actually _real,_ and his feet were moving faster now, he had never really thought about seeing it, it had just been a story, just old pictures, but now it was real and he was stepping out of the cave next to his brother and his dad and there was fresh air against his bones and cold and wetness and he looked up and …

Rain.

It was raining.

But it wasn’t like the rain in Waterfall. There, the rain was just water dripping from the cavern ceiling. Heavy and light, depending on the day and time, sometimes overwhelming, they had always called it rain, but Sans knew from the books he read as a kid that it wasn’t the same thing.

It hadn’t mattered then.

It was all just water anyway, right?

But …

This was rain. This was _real_ rain, water that had evaporated and formed into clouds and condensed until it was so heavy it had to fall to the ground. He looked up and he saw clouds, fluffy, dark gray clouds, the droplets of water falling into his eyesockets and over his cheekbones and onto his hands and he didn’t know if it was cold or warm and his clothes were soaked but god, he didn’t care, because this was _rain._

He turned to see Papyrus completely still, his sockets wide, his mouth barely open, his hands held up to catch the raindrops as he peered up at the sky. He had never looked so quiet, so wonder-struck—or maybe this him had, no matter how difficult it was for Sans to imagine. If he loved rain this much … it didn’t rain forever on the surface, did it? There was all kinds of weather. Sunny and snowy and hot and cold and rainy and—

“Come on. There’s something down there.”

Sans jerked his head back to Gaster, and all at once, the spell was broken as he watched the tall skeleton in the black coat stride down the side of the mountain. Had he even paused to feel the rain? Had he stopped to _remember_ what it was like to feel this _all the time,_ he had been alive then, he must _remember, this_ was what he had wanted them to see so bad, now they were _here_ and he wasn’t even _hesitating—_

But Papyrus was already bounding forward, and Sans found himself trailing behind them, his steps just quick enough so as not to be left behind.

Even with the rain obscuring his vision, Sans could still see how far the land stretched out in front of them. And that was just a tiny spec of it. Earth … the planet they lived on … it was enormous, from the books he had read. It looked so flat from here, but it was _round_ and beyond the line where the sky met the ground—the horizon, that was what it was called—there was a whole other _world._ Other places where it was raining, places where it _wasn’t,_ every kind of weather was happening _right now,_ all around the planet. So much to see. Maybe more than he could see in a lifetime.

His feet squished in the muddy ground, sliding occasionally but always holding him up. He stayed close to Papyrus’s side while Gaster walked ahead of them, his steps far more certain while Sans felt like he was wandering around in a pitch-black room.

It was … it was overwhelming, how did humans know what to _do_ with themselves with so much space, he could go in any direction and just keep going forever, never running out of room to move, places to see. There were trees in one direction, and buildings in another, far off in the distance—was it that far? Maybe it was closer, it wasn’t like he was used to looking that far in any direction—some of them tall, the name “skyscrapers” came to mind from one of the human books he had read, but others were small, like the ones in the underground, one or two stories, houses, roads, a _town._ All of them so far below.

Below.

Right. The underground was inside a mountain.

He had known that. Of course he had known that, that was how it had _caved in_ on them, but he had never really _imagined_ …

This had been his whole world. Just this mountain. And all this time, all of _this,_ it had been … it was right here his entire life, and now … now …

Papyrus and Gaster kept moving, and Sans followed them without a word.

It was a long walk down the mountain. Or at least it must have been—Sans was far too distracted staring at his surroundings to notice. He had never seen anything this tall—even the drop from the edge of the cliffs in Hotland. There were no gentle slopes guiding him down a natural structure. There was no grass, no mud, no trees, no bushes, no sky, no …

No rain.

He had never really taken the time to imagine it before. It had just been an idea, something he read about, something he dreamed about but never genuinely believed, even for a second, he would ever get to see. After a point, when he had given up on the initial experiments—when he had discovered what Gaster had done to replace them—he had stopped thinking about it entirely.

And here it was.

None of them spoke as they walked. Sans spared the occasional glance to Papyrus, still walking at his side, looking around at the sights with curious, baffled wonder in his eyes. Sans wasn’t even sure if he knew what he was looking at.

Suddenly, Sans remembered a much younger version of his brother holding up a picture of a car in one of his books, proudly declaring that this was what he wanted to have when he grew up.

Their dad hadn’t had the heart to tell him he would never see a real one.

And then he _might_ have, he was _going_ to, and Sans … and Gaster …

Did this Papyrus even want to see cars like Sans’s did?

The slope smoothed out after a while, and the thick trees began to grow thinner. The buildings looked far taller now, impossibly tall, how could anyone _build_ that high? He could see the smaller ones nearer to the mountain, and the roads, the town that grew closer and closer by the second. And bit by bit, Sans could make them out, first just little dots, but even with only one good eye, he could still recognize the shapes of the people that wandered the roads on the outskirts of the small town.

Monsters.

Smooth lizard monsters with long tails and furry monsters and tall monsters and short, tiny monsters and large goopy monsters and …

Humans.

Those were humans, weren’t they? It was hard to tell, but with every step he took, the clearer it became. Gaster had stopped walking in front of him, probably at his side now, but all Sans could do was walk forward.

No one was fighting. There were no screams, no sign of distress or conflict.

Did that human just wave at a monster?

Did the monster just wave back?

They were smiling.

They were … all of them …

Sans found his feet slowing, his eyes locked on the buildings around him, the bustle of people in the distance. Just like he thought, there were humans, or what he was fairly sure were humans, but … there were even more monsters. Monsters of all ages and shapes and sizes, he didn’t know their faces but they weren’t that different from the people he knew.

Monsters. On the surface.

In a town.

 _Their_ town.

They had _built_ this town. They had … they had gotten past the barrier, they had broken it, they had gotten _out,_ and they had built their own _town._

A home.

A home with the humans.

And now …

Why was Gaster here? What did he want? These monsters had gotten out, so they had already used the souls, hadn’t they? Or …

But if they had gotten out, if they were living with the humans … wouldn’t the humans hate them if they had come out using the souls of seven dead people? Would they know? How else could they have broken the barrier?

He turned to his left, the words already building behind his teeth.

But Gaster wasn’t there.

Sans blinked. He turned to his left, ready to ask Papyrus where he had gone, they had to find him, they couldn’t leave him loose in a place like this.

Papyrus was gone.

Had they … he hadn’t been paying attention to them, but surely he would have noticed if they had gone a different direction? Surely they would have noticed if he had wandered off? But … they had been staring at their surroundings, just like he had been. They had been distracted. Just like he had been.

Enough to walk off without him.

He turned from side to side, searching for any sign of white bone, but there was none. His breath sped up, his head spun, and suddenly he felt more alone than he had in his entire life.

“papyrus?” he called. Nothing. “papyrus? bro?”

Silence.

“papyrus?!”

“Hello?”

Sans spun around so fast he almost fell over. He searched for the voice, scanning the landscape through the rain to find the source of it.

And he did.

Papyrus, maybe ten yards away, walking toward him with his bright red boots squishing in the mud, looking back and forth as if to find the one who had called his name. Sans’s shoulders fell, his soul lifting, as he stepped forward to call his brother’s name—

Red boots.

His brother wasn’t wearing red boots.

Or an orange rain coat.

And he was _sure_ he had been wearing gloves.

Sans moved on reflex, not even thinking, scrambling behind the closest tree and ducking out of sight. The footsteps squished closer, probably only five yards away, closer, closer, then slowing to a stop.

“Sans?” his brother— _not_ his brother—called. “Sans, was that you?”

Sans started to talk, but swallowed his own words, gritting his teeth as hard as he could to keep any sound from coming out. He peeked around the tree to see Papyrus frowning, looking from side to side, searching for the source of the voice.

Then more footsteps squished in the mud nearby, and both Sans and Papyrus turned to face them at once.

“You called, bro?”

And Sans saw himself.

Himself, with hands stuffed in his pockets as he strolled up to Papyrus with soft eyes and a casual grin.

“Sans!” Papyrus called back, turning away from the Sans behind the tree and back toward the Sans that could only be his brother. He put his hands on his hips and glanced over his shoulder. “Weren’t you just calling me from over there?”

The other Sans looked over Papyrus’s shoulder, furrowed his browbone, then looked to Papyrus again.

“Uh … I don’t think so. Unless I forgot.”

Papyrus stared for a second, turned in the vague direction of Sans, and frowned. “Huh. That’s strange. I could have sworn I heard you calling for me.”

Again, the other Sans followed his gaze. He took a step forward, toward the tree Sans stood behind, his eyes searching, and for a second, Sans stiffened, and found himself wondering if he had the energy to outrun his clone.

“Is everything alright, boys?”

Then a voice called out from just behind the other two skeletons, and both of them turned to face it. Only as the panic began to slip from Sans’s soul did he shift his gaze to see the person approaching.

And he stopped again.

Because he was looking at his dad.

Sans knew it wasn’t. He _knew_ it wasn’t, it only made sense, if there was a Sans and Papyrus in this universe, of course there would be a Gaster, of course it was _their_ Gaster, not _his_ Gaster but Sans looked at him and his eyes were so gentle and his smile so soft and just a little concerned and when was the last time Sans had seen that look on his dad’s face, when had he last had _any_ hope that he would ever see it again—

“I think Papyrus is hearing things,” the other Sans piped in, jabbing a finger over his shoulder, toward his brother, as their dad stopped in front of them.

Their dad smirked just as Papyrus put his hands on his hips and frowned.

“I am not! Unless you mean I’m hearing real things, in which case, yes, I was! Your voice! Over there!”

He pointed in the general direction of Sans, and Sans felt his body go so stiff he swore he had actually turned to stone. The other Sans turned to face them, followed by their Gaster, but apparently they couldn’t quite make out Sans from the cover of the trees, because a second later, they were looking at Papyrus again.

“Perhaps Sans has been learning to throw his voice?” Gaster suggested. “Weren’t you talking about learning to, Sans?”

“You can do that?” Papyrus asked, annoyance overrun by curiosity.

The other Sans shrugged.

“Apparently. I met this group of humans last week and they can all do it. They even said they’d give me lessons if I teach them some stuff about monsters.”

“Hm,” Gaster replied, his expression soft and thoughtful and interested and Sans _knew_ that expression, he had seen it so many times growing up, mischievous yet intrigued and had his dad’s curiosity always looked so much like this own? “I’ll have to go and speak with them.”

The other Sans raised one half of his browbone. “What? You wanna learn to throw your voice?”

Gaster hummed and shrugged. “Oh, it might be a useful skill.”

The other Sans looked at Papyrus. Papyrus looked back. For a second, some sort of silent conversation seemed to pass between them, before the other Sans turned to Gaster again, his smile twitched into something like a grimace.

“Actually … maybe I’ll warn them not to talk to you,” he drawled, and Sans barely caught the humor in his voice. “Not sure I like the idea of you being able to make awful jokes from any direction you want.”

Gaster gave an overly-dramatic gasp, putting a scandalized hand to his chest even as he struggled to keep the smile off his face. “You wouldn’t do something like that to your own father.”

“Oh, that’s a good point!” Papyrus added in, grinning just as wide as his brother. “Maybe if I bake a cake for them, they’ll turn him away!”

“Betrayed by both my sons!” Gaster replied, pressing the hand closer to his chest. He could no longer hide his own grin.

Papyrus bit back an obvious snicker and shook his head with a mock-stern expression.

“I’m sorry, Dad, but I can’t risk the potential catastrophe of you being able to pun without me even being sure which direction to yell at.”

Gaster’s smile twisted into something closer to a smirk. “You always laugh, you can’t tell me my jokes aren’t _humerus._ ”

“Dad!” Papyrus whined, and Sans hated it, god he hated it and he loved it and that was _them_ and he wanted to run forward and collapse into their arms and he would be home, that was them, that was _them._ Papyrus turned to his right, frowning even deeper. “ Sans, stop grinning, you’ll encourage him!”

And for a second, Sans swore he was talking to him. Then he followed Papyrus’s gaze to the see the other Sans smiling just a little wider than usual, giving a half-hearted shrug.

“That’s just my face, bro.”

“No it’s not!” Papyrus shot back. “Your laughing smile and your not-laughing smile are completely different!”

“They’re exactly the same,” the other Sans retorted.

Papyrus lifted his head and grinned in something like pride. “Perhaps in your eyes they are, but not in mine. I’m your brother. I know you best.”

“I would think it would be I who knows both of you best, given that I’ve known you the longest,” Gaster piped in.

The other Sans shrugged again. “Eh, semantics.”

Gaster frowned and raised half his browbone. “I thought you were disagreeing with him?”

The other Sans shot him a much wider grin, his eyes gleaming with amusement.

“Not when it’s more fun to disagree with you.”

Gaster huffed a long, heavy sigh and shook his head, but his smile hadn’t slipped.

“Ugh, sometimes I can’t believe I raised both of you.”

But a second later his arms were slipping around each of their shoulders, tugging them in a little closer as they started back toward the town, their pace slow and leisurely, their continued conversation and laughter dulling as Sans’s eyes focused on the second tallest member of the painfully-familiar family.

This Papyrus … he was almost the same. Not exactly, no one would _ever_ be exactly the same, but he was _so damn close_ to the brother Sans remembered. And he was _right there._

Sans was fast. He was strong—strong enough, anyway. And he had the advantage. Maybe he couldn’t do it now, but maybe tonight, when they were asleep, if he snuck in and managed to sneak Papyrus out without waking him up, Gaster had managed it, Sans could get him back to their universe. It would take some explaining, he would have to make up a few lies, but then he would have him back, all the good without any of the pain and the trauma and the _broken look on his face,_ he would get his brother back, he would have _two_ Papyruses, and if he could make Gaster happy, if he could fix that one little problem, he would—

Sans stopped.

And he looked.

Looked at Papyrus, and the other Sans, and Gaster.

They had looked like that. Him, and his brother, and his dad. Just a few months ago. They had walked through Hotland looking like that perfect happy family and _Sans was thinking about taking one of them away._

Taking Papyrus away.

Like _his_ Papyrus was taken away.

He was …

… what the hell was _wrong_ with him?

That was what Gaster had done. Sans had hated it, that was what _Gaster_ had done, he had thought it was okay to just go to someone else’s universe and steal someone who didn’t belong to them, someone who had a family of his own, who had a _life_ of his own, someone who didn’t _belong_ in their world but Gaster had taken him anyway and now Sans …

Sans was going to do that.

He had really thought about it. He had really _considered_ it. He had looked at this Papyrus and saw his brother and he wanted him back, god he wanted him back and it would have been _so easy_ they were all _right there_ everything he had lost the life that had been ripped away from him his dad and his brother and why should the other Sans have what he couldn’t but he couldn’t take them away from where they belonged and he couldn’t stay no matter how badly he wanted to but …

But …

“Sans.”

Sans jumped, harder than he knew he _could_ jump after he had been walking for so long. He spun around, stumbling, almost falling, his breath coming so fast it hurt, he knew he didn’t need to breathe but it was habit, supposed to be comforting even though it made his ribs ache. His body wobbled, his head fuzzy as his eyes struggled to focus on the figure striding back toward him.

Dad.

But … no, Dad was already … he had gone back toward …

Dad and Pap and _him_ …

This wasn’t Dad. Or … _that_ wasn’t Dad, or neither of them, or both of them, but the man walking toward him now didn’t look right, he wore the same clothes, he had the same face, but his expression was cold and hard and calculating and there should have been affection shining in those eyes but there was none.

Sans hadn’t realized how much he had forgotten what that affection looked like.

He hadn’t realized how such a short glimpse could make him miss it.

He blinked, and it was just him, and Gaster, standing in the rain, the water dripping over their skulls and their clothes, perhaps a quarter of a mile out from a human town.

Papyrus was behind him. Far behind him, like he had gotten distracted looking at something or maybe he had just gotten separated from Gaster and in any case Gaster wasn’t paying attention to him, he just walked like he assumed Papyrus would be there, just like he talked like he assumed Sans should have been at his side the whole time.

And Papyrus was left running toward them, scrambling to catch up.

Sans didn’t need to see him up close to be sure of the worried expression on his face.

The worry, the fear, that he would be left behind.

“Stop dawdling and hurry,” Gaster said, snapping Sans’s attention back to him. But Gaster didn’t walk all the way up to Sans. Instead, he turned toward the town, not striding right into it, but peering out among all the people there. He hummed, and started forward again. “There are plenty of humans here. It won’t be as easy as I had hoped, but at least we’ll have the element of surprise. I doubt Papyrus will be much help here, but with the both of us, we should be able to—”

“wait—they—the humans—they’re _fine,_ gaster,” Sans stuttered out, stumbling over his own words as he struggled to get his head, and his voice, to work right again.

Gaster stopped. He turned to face him, his browbone furrowed, his eyelights narrowed in the most genuine confusion Sans had seen on his face in weeks.

“I beg your pardon?”

Sans shook his head, huffing breaths in and out as he forced his mind to settle. He looked back toward the town. If he squinted, he could still see the faint forms of three skeletons off in the distance, walking together, back toward home.

“they’re not … they’re getting _along_ ,” he went on, turning to Gaster again. “look at them, no one’s fighting, no one’s killing each other! they’re … they’re _peaceful._ ”

Humans and monsters. Monsters and humans. Living in one town, _together._

Like they used to, a long, long time ago.

Like Sans, and everyone else, had been so sure they never could again.

Gaster should have recognized it. Should have looked at it and seen what he had _already_ seen, seen what he had _grown up with,_ seen the human who had been his friend even if she had betrayed him, even if he was still mad, even if he didn’t believe this could last, he should look at it and at least _care_ but he …

He just looked back at him with the same confusion as before.

“And what difference does that make?”

Sans stared, and found his traitorous eyes flicking to Papyrus, still too far off in the distance to hear them, but getting closer fast. Sans shook his head and looked to Gaster again.

“we … the monsters here, they’re not fighting the humans,” he said. He motioned toward the village, trying to make Gaster see it, _really_ see it, he was looking at it but he _wasn’t seeing it_. “ the humans aren’t trying to hurt them. if you … if you _kill_ one of them, if they find out what you did, they’ll … they’ll think _these_ monsters did it! it’ll ruin everything they’ve got here!”

“I don’t see how that’s any business of ours.”

It came out so quickly, so nonchalant, that even with as much as he had changed over the past few months, as little as he reminded Sans of who he had been before, as much as he had lost, as much as he might _never_ get back … Sans almost couldn’t believe he had actually heard it.

Then, for the briefest of seconds, something like guilt flashed across his dad’s face.

And it was gone.

He looked away.

“They’ll manage,” he muttered, matter-of-fact, but not quite as confident as before. He straightened up and gave Sans another glance before turning to the town again. “And humans are bound to betray them at one point or another, we’d only be speeding up the process.”

Sans’s breath was coming too fast now, his eyes flicking between the town and his da—not his dad, not his dad, _never his dad again_ —

“are you even _listening_ to yourself?!” he spat. Gaster’s head snapped to face him, but Sans didn’t pause, didn’t care, even though he looked at those damn eyes and he could see the other man, he could see his dad, he could see someone who loved him, who cared for him, who _ruined everything and was about to ruin everything for another him, too_ —He grit his teeth and curled his hands into fists, jabbing one arm where he had last seen his other family. “those are _people_! _real people_! every one of these parallel universes, every one of these people, they’re not just … _spares,_ they’re … they’re _real actual people,_ and you’re gonna ruin _everything_ for them, _everything_ they’ve worked for! you’re just gonna waltz in here and take it all away like it _belongs_ to you, but it _doesn’t_! _none_ of this is ours! _they_ made it up here! _they_ got to the surface! _they_ made peace with the humans! and you think just cause you have a machine that can _take_ you here, you can yank it all out from under their feet! but you _can’t_! it doesn’t _belong_ to you! not the human souls, not the life they have here, not their perfect happy families, not papyrus—”

“SANS?”

Sans stopped, and he didn’t even have to turn his head to see the owner of the voice staring back at him.

Papyrus had stopped only a few feet behind Gaster, a few _feet,_ yet somehow Sans hadn’t noticed him. His browbone had creased, his mouth pressed into a tight, worried line, one of his feet already leaning forward as if it was all he could do not to run forward and pull Sans into a hug.

“SANS, WHAT ARE YOU SHOUTING ABOUT?” he asked, even though he must have heard, he was too close _not_ to have heard. “WHAT’S WRONG?”

Sans floundered. He couldn’t lie. He couldn’t _not_ lie. He couldn’t lie because Papyrus had been close enough to hear the truth, he wasn’t deaf, he wasn’t stupid, he must have heard, even if he wasn’t admitting it now, but every time Sans tried to think of a way to tell the truth his throat went blank.

Papyrus must have seen what this Gaster was like by now.

He _had_ seen what this Gaster was like by now.

There was no affection lost. This wasn’t his dad, this had _never_ been his dad. He had nothing to lose.

But Sans couldn’t bring himself to tell him.

And before Sans could think of a single word to push past his teeth, Gaster huffed and shook his head.

“We don’t have time for this,” he said. There was something in his voice, something off, something Sans almost would have called pained if he hadn’t known any better. But Sans didn’t get the chance to check his expression to see if there was any sign of it there. He was already turning away, back toward the town, back toward the humans, toward the monsters, _toward his family._ “We’re lucky you haven’t already drawn attention to us. Come on. There must be something we can store the souls in around here. Two or three should do it, then we—”

Before he could take another step, Sans reached forward, grabbed his arm and threw his weight back, dragging Gaster with him. Gaster stumbled before jerking around to face him, eyes wide, mouth open, his cold certainty replaced, just for a moment, with shock. Then he tugged back, starting forward, even as Sans struggled to keep him in place.

No. No, he couldn’t let him do it. He had already ruined one universe, Sans _wouldn’t_ let him ruin another.

Not this one.

Not this one place where everything was alright.

Not this one place where him and Papyrus and their dad—

Sans pulled harder, but Gaster expected it now, and this time he didn’t budge an inch. He was stronger. He had always been stronger, and now Sans was so damn _weak_ and Gaster was moving forward now, barely impaired, even as Sans struggled and kicked the muddy ground and gripped him as tight as he could, he couldn’t stop him, he _couldn’t stop him, he had to stop him,_ Papyrus was racing toward him, saying something, what was he saying, his hand was on his shoulder, and Gaster was turning, ready to push both of them off at once, no, they had to get away, get back, _get back to the machine_ —

Sans jerked back, and the world split down the middle.

Or, at least, that was what it felt like. Like every atom of his body was being ripped apart and shoved back together at once, like he was everywhere and nowhere at the same time, like he couldn’t breathe, he couldn’t move, he couldn’t think, he was dying, he had to be dying, but he could still feel his brother and Gaster and—

Then it was over.

And all three of them collapsed in a heap on the floor.

The cold, hard, _dry_ floor.

Sans groaned, pressing his hands to his skull, vaguely aware of the two other people groaning and shifting at his sides. He squeezed his sockets shut, then blinked them open, bit by bit, his eyes adjusting to the lights around them.

The lights.

It had been dark before. Not as dark as night, but definitely darker than _this._ And it had been wet, and the ground was squishy, and there hadn’t been any smooth, solid floor in sight a second ago, so where the hell had it come from?

He opened his eyes all the way and tilted his head to the side to look around at the room.

Because it _was_ a room. A small room with no windows and one door.

And one machine, only a few feet from where he now lay.

The lab.

They were back in the lab.

What must have been at least half an hour’s walk, if not a full hour or more, _seconds_ ago they had been right next to the town and now they were …

“What was that?”

The voice was quiet even as it demanded attention, demanded _answers,_ even as the owner pushed himself to his feet. Sans lifted his own head, slow, shaky, to meet Gaster’s eyes, wide and frantic and terrified and _fascinated_ and Sans couldn’t even tell which emotion was winning.

It was real. Gaster saw it, too.

Gaster felt them move.

Gaster felt them … _jump._

“How did you do that?” Gaster went on, stepping forward again. Sans let his eyes drift to the side, seeking out Papyrus as he pushed himself up on trembling arms, staring at Sans and Gaster with so much fear, he was _so damn afraid_ and Sans had _made_ him afraid Papyrus shouldn’t have seen all of this he _never_ should have seen all of this Sans just got him back and it had taken him just over a day to ruin everything all over again. Gaster took another step, eyes wide, the lights in them gleaming with interest.

Interest that wasn’t going to let him go until it was sated.

“How long have you been able to—”

Sans didn’t wait for him to finish.

He threw himself off the floor, slamming into Gaster’s still-unsteady body and knocking him through the open door, into the machine.

Gaster fought back, grappling with him, hand-to-hand combat neither of them had ever learned. They slammed each other into the walls, trying to gain control, but neither let the other go long enough to summon a bone or even latch onto the other’s soul. Sans was weak, weaker than he had ever been, but Gaster’s magical strength didn’t extend to his body. Every time he started to get the upper hand, Sans would shove him away or pin him down or make that one unexpected, thoughtless move that caught him off-guard.

Sans could hear the footsteps, the calls, make out his brother’s voice begging them to stop, even feel his gloved hands grabbing at him, but Gaster wouldn’t let go and if Gaster wouldn’t let go neither could Sans he couldn’t let him win he couldn’t let him win this he just wanted to go home he just wanted to get out of—

They tumbled into the machine, slamming into the back wall of the inside, Papyrus chasing after them even though there was barely enough space with them fighting. In the back of his mind, Sans registered the ache in his bones, he was too tired to fight, he was too tired for anything, but he couldn’t stop, he couldn’t let Gaster win, couldn’t let him take away everything that these people had worked for even though Sans had been so ready to grab the other Papyrus and take him home so ready to go to every goddamn universe and find every Papyrus and take them because he wanted his brother back and he would _never get him back and_ —

Sans shoved Gaster to the side, and only realized when the humming began that “the side” had been the control panel.

He stopped, and he only had a second to fear that Gaster would take advantage of his shock before he realized that Gaster had frozen, too. Sans stepped back, giving Gaster room to turn around and look behind him on the spot where he had landed.

“what’s happening?” Sans breathed. “what did you hit?”

Gaster didn’t respond. He just stared at the control panel, humming, lighting up.

Almost without a thought, Sans reached out and yanked the machine door shut.

And only a second later, the machine began to shake.

Like in the sci-fi novels and movies Sans had soaked up when he was a kid, like the machine was flying through a literal wormhole, through a timestream, but that _wasn’t how it worked_ the machine shouldn’t have moved unless they pushed it, except they _had_ pushed it and then they had pushed some button and now the machine was running, the control panel lighting up and the floor beneath him rocked more by the second, shaking, side to side, up and down, like they were being tossed around as clothes in a dryer.

Sans threw out his arms, grabbing for something, anything to hold onto, but the machine didn’t have any handles, he had never had time to _build_ anything like handles or seats or safety belts, but when he felt a bone against his hand he grabbed it and he didn’t know if it was Gaster or Papyrus and he didn’t _care_ he couldn’t let it go and it didn’t pull away.

They tumbled and spun and the machine shouldn’t have been upright after all this but it hadn’t fallen over it didn’t feel like it even _could_ fall over like there was no gravity there was no up or down there was nothing at all except the warm bones clutching him, they were going to die, they were all going to die in this stupid machine and he could have just let Gaster take those souls and wreck everything why did it matter why did anything matter it would all be over and none of them would have to hurt anyone and—

There was no thud. No crash. No sign of an impact.

The flashing lights went dark.

The humming faded to a buzz before going silent.

Then everything was still.


	46. Chapter 38

**Notes for the Chapter:**

> Just realized I haven't thanked all you guys at once for a while. So thank you. :)

Something was wrong.

Something was very, very, very, _very_ wrong.

Sans breathed. All he could do was breathe, and even that felt wrong. He knew he must be hurt, he had slammed hard enough into the wall of the machine, and with his low HP, it was probably a miracle he hadn’t died then and there. But it didn’t matter. Nothing mattered because everything was wrong and he had to get away but there was nowhere to go Gaster had let go of him but he couldn’t get out, he wanted to run, but his body wouldn’t _move_.

The lights on the machine barely illuminated the two people around him. Papyrus, to his left, and Gaster just in front of him, turned away, he was so close but he might as well have been standing on the other side of a crowded room for how much attention he paid Sans.

Sans would have thought he would be used to that by now.

Gaster was moving. Not much, there was hardly any room to move in here, but he was moving toward the door, reaching out his hand, no, no no no no _no,_ they had to get out, just punch the numbers into the machine and get out of here, they didn’t need to see what was out there, Sans didn’t _want_ to see what was out there.

“gaster,” he bit out, the sound coming out as little more than a croak through his clenched teeth and tight throat. Gaster didn’t respond. Sans stiffened further. “gaster, stop. you … don’t open that, okay? something’s wrong.”

Gaster’s hand paused for less than a second before it tightened around the handle and pushed it down, letting the door creak open. Had the hinges sounded so rusty before? He could have sworn it was silent in the lab when they had come out in all the other universes, but this was worse than silence, it was _nothing,_ and he could hear every breath, every twitch, every inch the door moved and it was like _screaming._

“gaster!”

No reply.

Gaster let his hand fall away from the door, staring out into the darkness beyond.

“dad!” Sans choked.

Silence.

He could feel Papyrus close to his side as he leaned toward the exit, ignoring every instinct to get away, stay away, stay far _far_ away from whatever the hell was out there. He didn’t get it, he couldn’t hear anything, he couldn’t see anything, it didn’t feel like all the dead worlds, it didn’t feel like anything, it felt like …

Like …

Sans peered over Gaster’s shoulder, and his browbone smoothed out as his breath left him all at once.

It was … nothing.

Nothing … at all.

No ceiling. No walls, no floor. No room. No exit. No light, except for the vague glow that came from within the machine. Gaster reached his foot out, and for a second, Sans swore he was going to fall into the nothing, plummet into an endless abyss. Then his foot stopped. Not with the tap that might be expected of someone touching a floor. It just … stopped.

And he kept walking.

Sans stared after him for a good ten seconds. He looked at Papyrus, who gripped his arms and gazed out through the open doorway with sockets as wide as Sans had ever seen them.

Then Sans took a deep breath and followed Gaster out into the darkness.

“SANS!”

Sans wanted to stop. He wanted to turn around and run into the machine and back to his brother and this was their chance, wasn’t it, they could get away, they could leave him here, they would never have to deal with him again, they could run and find somewhere else where they would be safe and no one would _ever_ hurt his brother again but—

But—

Sans kept moving, his eyes locked on Gaster several feet ahead.

He barely noticed the faint sound of breath behind him as Papyrus rushed to catch up.

Gaster stopped walking so suddenly Sans almost crashed into him. He scanned their surroundings, empty, dark, for anything he could have seen that would make him stop, but there was nothing, _nothing,_ and Gaster was just standing there staring out at the black void, everywhere, it was _everywhere,_ it never ended, what if they turned around and the machine had disappeared, what if they were stuck here forever and—

“Entry number seventeen,” Gaster murmured, even though his clipboard hung uselessly in his hand at his side, apparently forgotten. His eyes locked ahead of him, on the overwhelming shadows, as if he could see something in them.

Sans wrapped his arms around his torso, squeezing himself, as if he was cold. But … he didn’t get cold, did he? Not really. He could feel the temperature, but it never _bothered_ him, but this was … was this what other people felt when they talked about cold? Covering his whole body, seeping into the depths of his bones, the feeling in his limbs numbed, his mind fuzzy, his vision faded, no, that was just the darkness, everything was dark, he could see Gaster perfectly, Papyrus at his side, but everything else was nothing but black and—

“Dark, darker, yet darker.”

Sans stiffened even further.

It was his dad’s voice. It was Gaster’s voice. But … it wasn’t.

It was … different.

Different than all the experiments, distant, cold, like he was still him but he was someone else at the same time and it was _wrong_ and Sans didn’t know why and it hurt to hear, it hurt to _think_ about, and all Sans had wanted was his dad to look at him but now the thought of seeing his face had never felt more terrifying.

Gaster stared out into the abyss, his head high, his body limp.

“The darkness keeps growing. The shadows cutting deeper. Photon readings negative.”

It was wrong, wrong wrong _wrong._

Gaster’s hands were at his sides.

He wasn’t looking at the measurement device.

So how did he …?

“This next experiment seems very very interesting … what do you two think?”

Sans couldn’t breathe.

They had to get out. Out out out he didn’t want to _be_ here anymore this was all wrong he didn’t want to be here he _shouldn’t_ be here no one should ever be in this goddamn place and Papyrus was here and _he wouldn’t let him hurt his brother again._

“gaster,” he spat, and even though his breath was shaking, his voice, by some miracle, came out steady. He held himself a little taller, letting the bubbling heat build in his bones, in his soul, the bubbling heat that had scorched him every time the needle poked into his arm or he got ready to fire off a blaster. It was power. It was security. And he welcomed it. He reached out a hand, letting the magic focus it his soul, and wrapped it ever-so-slowly around Gaster’s, as if there was a chance he wouldn’t notice if he was careful enough. “we’re leaving. c’mon.”

He expected resistance, if anything at all. Sans had never practiced his blue magic much, and aside from that one strike in the lab—it seemed like forever ago—he had never really used it outside of training. He knew Gaster could fight against him, if he wanted to. Sans could pull at his soul all he liked, and if Gaster didn’t _want_ to move, he wouldn’t.

But he did.

He took one step back, then another, then slowly, uncomfortably slowly, turned to face him.

It was still his face. But … it was like his voice. Blank. Distant.

It was his face, but it didn’t _look_ like his face.

Not that it had looked like his face in a very long time anyway.

Sans started backward, not bothering to keep a hold on his soul as his dad walked on his own. He glanced over his shoulder every couple of seconds to make sure he wouldn’t stop, but Gaster never did.

He never looked at him either. He just stared ahead, his eyes as distant and blank as before.

It didn’t matter. As long as they left, nothing mattered.

Sans stepped back into the machine, followed immediately by Papyrus, and a second later, by Gaster. Sans wanted to yank the door shut, but Gaster took his sweet time, staring out at the darkness like it was calling him. Maybe it was. Sans didn’t know. He wasn’t even sure he cared.

He wanted to go home. He wanted to get out of here, get out of this machine, get out of the lab, just go back to the house and hide in his room and never, ever leave again. He wanted to take Papyrus and run like he should have done from the beginning, there was no going back now, he would never be able to get his dad back, his dad was _gone,_ Papyrus was gone but he was still here and Sans couldn’t risk losing him again.

He watched Gaster punch numbers into the machine, his movements slower, more robotic than before. He didn’t pay attention to what the console said. It wasn’t like it would have made any difference. None of them knew where they were going.

And anywhere was better than here.

Fingers brushed his own, and this time, Sans didn’t even hesitate before squeezing his brother’s hand in return.

This time, he had no doubt they were both shaking.

Gaster stepped away from the console, and the machine began to buzz. But unlike the anxiety that had filled him every time they set off before, now, all Sans could feel was relief.

They were getting away. They were getting out of here, and they were never coming back.

But … Gaster might.

He _liked_ that place. He was … interested by it. Even if he let them leave now, he would surely want to come back another time. And he would drag Sans and Papyrus there again. Sans didn’t know what was wrong with it, it was dark, it was silent, it was too much of both things, but there was nothing _else._ Except there _was._ Something he couldn’t name but he _knew_ something was wrong and the longer he stayed there the worse it got and he would rather die than step foot there again.

And even if Gaster _didn’t_ take them back …

He would go back to looking for the souls.

Exactly like he had done before.

He would go back to that universe on the surface. He had the coordinates, he could go there anytime he wanted, Sans wasn’t even sure he wasn’t going there _now._ He had punched in the same buttons as before, it didn’t _look_ like he was picking a number intentionally, just … doing the same apparently random control sequence as he had since this trip began. Letting the machine decide on a place to take them, since there were far too many unexplored universes for them to know where to tell it to go. But he couldn’t be sure. He still didn’t know all that Gaster had changed about the machine. He hardly knew anything anymore.

Part of him almost hoped that they were going back to that universe. At least going there would mean he was back to his old goals. At least going there would mean he had forgotten about the dark place.

It had seemed so important before. Stop Gaster from getting the souls. Stop Gaster from destroying another universe’s future, another universe’s _happy ending._ But … it wasn’t _their_ happy ending. It was, but it _wasn’t,_ Sans never had to know what happened to them, he never had to think about it, he _would,_ but he would _stop_ with time. He wouldn’t get a happy ending, he knew that, but he would be with his brother and they would be _safe_ and Gaster would get everyone out just like they wanted and Sans and Papyrus would find somewhere else to live on the surface far, far away from their da—from Gaster.

They would never have to see him again.

Funny, how that had seemed like such a bad thing before.

The machine jolted to a stop, but far more quietly than last time, and Sans gave Papyrus’s hand one more tight squeeze before forcing himself to let go.

Even if they did go to one of the other universes, even if Gaster went through with his plan to hunt down the souls by any means necessary … Sans and Papyrus would still be with him. If he made people mad—and he _would_ make people mad, if there was any chance of them realizing the souls were gone, if there was any chance of them realizing he had _murdered a human when they were getting along so well and ruined everything they worked for_ …

Sans and Papyrus would be blamed as well.

There was no avoiding it. No escaping it. If they were with Gaster, they were targets.

And Gaster had already proven that he didn’t give a second thought for their safety.

He would let them get hurt. Maybe he wouldn’t _intend_ to, but it wasn’t like he was doing anything to _stop_ it. It wasn’t like he hadn’t already hurt them a hundred times before.

If Sans and Papyrus wanted to get out of this, if they wanted to get home safe, if they wanted to get home _at all_ …

Gaster reached for the handle of the door and, without a second’s hesitation, pushed it open.

It was the lab. No darkness. No emptiness. Just … the lab. Or something that looked like the lab. It was the same room, though it was dimmer. There were lights—it would have been pitch black otherwise—but they felt different, like there weren’t supposed to be lights but there _were_ supposed to be lights and the room couldn’t decide which it wanted. Gaster stepped out, pausing to glance around the room before he started toward the door, his measurement device clutched in one hand, his clipboard in the other, ready to explore this universe just like all the others, to drag them through world after world until he took the souls and dragged them back home but maybe he would never be done maybe Sans would never see his home again and maybe he would take them back to that dark place and …

And …

Sans felt the blaster materialize behind him almost before he even realized he had left the machine himself.

“don’t move.”

Gaster stopped.

He didn’t flinch. Didn’t jolt. Didn’t turn around. He didn’t even look surprised, even though Sans couldn’t see his face to be sure.

He just stood there, with the sort of posture Sans had long come to recognize as mildly irritated.

“I’m really not in the mood for empty threats, Sans.”

Sans said nothing. Gaster waited, then took another step forward. The blaster shot forward, in front of Sans, and Sans barely held back a wince when Papyrus stumbled back to get out of the way. He kept his eyes on Gaster, his sockets almost completely black, his browbone low.

“i said don’t move,” he ground out.

Gaster didn’t move.

“SANS?”

Sans tensed. He hadn’t noticed Papyrus standing just to his right. How had he forgotten? He had been there the whole time, following them, he had been so quiet, why was he so _quiet,_ he couldn’t even tell if it was more or less like _his_ Papyrus, he had been so different for so long, he—

He turned to his brother, took in his confused, scared eyes, and tried to make his smile look at least a little reassuring, glancing back to Gaster every few seconds to make sure he hadn’t tried to move. “it’s okay, pap, just … stay there.”

He turned back to the Gaster in full, holding the blaster on him. But Papyrus took a step closer, even though Sans could see him watching the blaster with wide eyes out of the corner of his own gaze.

“WHAT’S GOING ON?” he asked, a nervous tilt to his voice that made Sans want to banish the blaster then and there. “WHAT IS THAT SKULL THING?”

Sans winced. But as much as his head ached to face his brother, he kept his eyes on Gaster, kept his hand up, just enough to be ready to blast him at a second’s notice. Even if he could barely imagine really doing it.

“i want you to take us home,” he said, and though his voice trembled, very faintly, he had never sounded more serious. More absolute. “right now. you can go back in your stupid machine, you can do whatever the hell you want, but you have to take us back. take us back and leave us alone. for good.”

Gaster turned his head, just enough to look over his shoulder and meet Sans’s eyes. His face was almost blank, save for a slight quirk to one side of his browbone. “You seemed very intent on coming with me at first.”

“you’re putting all of us in danger,” Sans shot back without missing a beat. His hand shook a little harder, and he had to swallow back the lump in his throat. “you’re being a careless idiot, and if you don’t care what happens to you, fine, but i _won’t_ let you drag my brother into this.”

“SANS …”

Papyrus’s voice was so quiet Sans could barely hear it, and even though he didn’t turn to face him he swore he could feel those startled eyes burning into him.

“I don’t think that would be very wise,” Gaster said, his voice slow, blank, painfully logical. Even with the blaster still hovering over Sans’s shoulder, Gaster didn’t look afraid.

Of course he didn’t. He had seen how little damage it did.

It would take dozens of consecutive blasts to even knock him down, and by then he could easily run away.

Sans lowered his hand just enough so the shaking wasn’t so obvious.

“it’d be a whole lot easier if you didn’t have the two of us following you everywhere.”

“But I may need your help,” Gaster replied. “Especially if I need to take the souls by force.”

Sans took a step to the left, and Gaster did the same, keeping the distance between them. Another step from Sans, another from Gaster.

“and you really think i’d be any help? in the _state_ i’m in?” Sans hissed.

Another step. One after that.

Gaster was moving. Just as Sans hoped, with every step Sans took toward him, around, circling toward the door, Gaster matched him, allowing himself to be herded back toward the machine whether he realized it or not. Sans had to bite back a bittersweet smirk. For a so-called genius, he sure was easy to fool. Sans might not have had strength, or even much higher intellect, but that didn’t mean he couldn’t get back the upper hand.

If his vague smugness showed on his face, Gaster didn’t notice it.

But he wasn’t speaking either. He didn’t reply to Sans’s question, but it didn’t seem to have stumped him. He looked like he was thinking.

Sans couldn’t remember the last time that look had meant anything good.

“And what if you should decide you don’t want me to come back, and destroy the machine while I’m away from it?” Gaster asked at last.

Sans made the closest thing to a frown that his body could achieve. “you’ll have it.”

“There is still a version of it in our universe,” Gaster said, even as Sans took another step and he moved to follow it. “There is _always_ a version of it in our universe. It is permanent. And it is only logical to assume that if it is damaged in one universe, it will be damaged in all.”

Sans started to speak, but stopped. He was right, even if Sans hadn’t thought of it, even if he wasn’t sure if he would have really done it. If there had been a chance, if he had realized it, if he had realized that he could stop all this hell by trapping Gaster in another universe, even if it meant this Papyrus would never go back home …

“You’re coming with me, Sans,” Gaster finished as Sans felt his own arms drop back to his sides. “This isn’t up for discussion.”

Sans grit his teeth and held his arm out a little higher.

“no. we’re. not.”

And as soon as the words left his mouth, Sans saw it.

Gaster had moved. Away from the door, back to the machine, until he stood right in front of it. Just as Sans had planned. Just as he had wanted.

But when Sans had moved, Papyrus hadn’t followed him.

He had stayed in front of the machine.

And now Gaster stood just beside him.

“Your brother is,” Gaster said, without even breaking eye contact, not even when Papyrus flinched and looked at him with wide, blinking eyes. “And you wouldn’t leave him here and go by yourself, would you?”

Sans had already been tense, but now he felt like a rock, he couldn’t move, he couldn’t think, Gaster was too close, get away from him, get _away_ —

“don’t you _dare_ —”

“I told you, Sans,” Gaster cut him off, flicking his eyes to Papyrus just long enough to make a point. “You’re coming with me.”

“get away from him!” Sans snapped, raising his hand to command the blaster.

Papyrus stiffened, eying the skull hovering over his shoulder with something like fear.

“SANS?”

Sans froze.

His hand lowered.

He had—he had almost—but Papyrus was _right there,_ Sans could see him, it didn’t matter which Papyrus it was, it was _Papyrus,_ he couldn’t—but if he hit Gaster, if there was any _chance_ it could do enough damage to matter—

“just … get back in the machine,” Sans bit out, eying Gaster with hard eyes that probably didn’t look half as threatening with his body shaking as much as it was. He swallowed and held himself taller still. “we go back home, you … you can lock us out of the lab, do what you want, but you’re taking us _home_! ”

It didn’t sound threatening. Not that he had really thought Gaster would be threatened, he knew too well for that, but Gaster still had _some_ sense of logic, some sense of self-preservation, even if he had thrown most of it to the curb, he had to listen, he _had_ to listen, but he was just standing there staring back at him with blank eyes that flicked over to Papyrus and …

And …

No. He wouldn’t hurt him, he _couldn’t_ hurt him, he had done so much to bring him back he had gone to another _universe_ to bring him back he had sounded so desperate so pained that had been _real_ he wouldn’t hurt him now he—

Sans didn’t know.

He didn’t know anything.

He didn’t know what Gaster would do or wouldn’t do. He could make all the threats he wanted, but if Gaster was willing to hurt Papyrus … if he was willing to go that far to get what he seemed _so sure_ was the _right_ thing to do …

Gaster let out a long, heavy sigh, and it took Sans a few seconds to process the fact that it sounded entirely genuine.

“I’m sorry, Sans,” he breathed, lifting his gaze to meet Sans’s, locking him in place as he took a step forward, away from the machine, back toward the door. As he moved, his hand reached out and grasped Papyrus’s arm, nudging him along with him, as Papyrus stared and moved on reflex, not sure whether he should obey but not having a reason not to. Gaster’s face set. “I’ve come this far. I’m not going to risk losing it all now.”

He couldn’t.

But he could.

He would.

He—

Sans’s hand was up again before he realized it had begun to move.

The blaster hummed, he swore it was growling, could blasters growl, he didn’t know, he didn’t _care._

His other hand grasped Papyrus’s soul, yanking him out of the way too fast for Gaster to realize he had moved.

Then the blaster fired.

Sans had only ever fired his blaster in one place: the lab. The lab was by no means huge, but it was big enough to hold as much equipment as Gaster could ever need for his work, as well as plenty of free space for experiments. And compared to the room that had been Sans’s private lab, it was enormous. There was room for an attack, even a strong attack, to be set off without causing damage to the rest of the room.

There was no room for that here.

And while Sans had always fired at a blank wall before, now, he was firing at a person.

The blast hit, and the whole room exploded in a cloud of dust and smoke.

Sans couldn’t see. He couldn’t see he couldn’t breathe he could feel Papyrus as he let his soul go he was fine he was alive he was out of the way he wasn’t hit but he _couldn’t see through the damn dust_ —

He coughed even though he had no lungs to cough the dust out of. Something was burning. Was that … no, Gaster would be making noise if it had burned him. Was that even how his blaster affected monsters? He had tried to hit Gaster, and it hadn’t worked, he was too weak, but some damage had been done, how much, had it changed when he absorbed the human soul, was he stronger now? Sans blinked hard, waving away the smoke closest to his face, squinting to see through the gray that filled the room.

Bit by bit, the smoke cleared.

But Gaster wasn’t there.

There were no bones on the ground, no sign that he had just fallen over, maybe he had run behind the machine, he was fast, he could have ducked out of the way, but …

The smoke cleared, and suddenly, it didn’t matter whether Gaster was there or not.

Because even if his blaster hadn’t hit Gaster, it had hit something else.

It had hit what was _behind_ Gaster.

It had hit the machine.

Sans stood there, his limbs beginning to shake as the rest of the dust dissipated and he finally made out the damage. The machine he had spent weeks on, the machine he had butchered from its original form, the machine that had brought them here, the _machine that would get them home_ …

The metal was warped in places, enough to break the screws holding it together. The control panel had been blown open, and he could already see several broken wires inside. Several more pieces had simply fallen off.

It was broken.

The machine was—

No. No no no no _no._ This wasn’t happening, this _couldn’t_ be happening, he couldn’t have done that, he wasn’t strong enough, sure he had absorbed the rest of the soul but it couldn’t make _that_ big a difference, he had hardly even felt it, it wasn’t like absorbing a whole soul, he was still weak, his HP couldn’t be higher than 2, _he wasn’t strong enough to do that much damage_ —

The smoke cleared all the way. Papyrus sat off to the side, staring at him, unscathed, not even a scratch.

And the machine was a wreck.

Sans had crossed the room before he even realized he was moving. His kneecaps stung as he hit the floor but he ignored them, scrambling to make out the damage, he could fix this, he _had_ to fix this, that was their only way home, he had built it, he could fix it, he just had to find all the pieces and …

And …

He stopped, staring into the inner workings he had pushed aside to examine, his hand frozen in a tangle of wires.

The core was gone.

_The core was gone._

He turned from side to side, running his hands over the mess on the floor, searching the wreckage for where it could have fallen, it was a glass ball filled with bright red liquid, it shouldn’t be that hard to find among hunks of gray metal. What if it had shattered? But he didn’t see any broken glass, didn’t see any red liquid on the floor, and he would have, _surely_ he would have, he just had to find it, that was what made the whole thing work, things had _changed_ once he added it, once he added the S.E., once Gaster added the _soul._

But it wasn’t there.

Papyrus was talking to him, saying something, he was right behind him but Sans couldn’t stop searching. He couldn’t lose it. He _had_ to find it, that was how they got home, that was the _only_ way they could get home, they couldn’t be stuck here, but he couldn’t find the pieces and he couldn’t even see any liquid on the floor he didn’t know where it was he had to get it back can’t be stuck here have to get home have to—

Sans stopped, arm already stretched out to push aside another piece of metal.

Gaster.

Gaster wasn’t here.

Not his body, not his bones, not even his _dust._

And neither was the core.

“SANS?”

Sans jerked his head around, blinking as his eyes refocused on his brother, standing just behind him, his hand hovering only a few inches above his shoulder, like he wasn’t sure whether to touch him in an attempt at comfort. His face was twisted into concern that Sans hated, he didn’t deserve it, he didn’t deserve _any_ of it, but he still soaked up the affection in those eyes like he was dying of thirst. The hand above his shoulder twitched, hesitated, then finally brushed the back of his hoodie in an uncertain attempt at comfort. For a second, Sans had to fight every instinct not to throw himself into Papyrus’s arms and just cling, cling like that would fix any of this, cling like he actually deserved that reassurance, cling like he hadn’t just screwed all of them over because he was _stupid_ enough to fight back when he had no chance.

He looked at the machine again. The smoking, twisted, undeniably _broken_ machine.

Their way home.

Their _only_ way home.

Sans’s legs trembled as he pushed himself to his feet, and he almost fell over again once he was standing straight. Papyrus’s eyes locked on him the whole time, but Sans refused to let himself look at him for more than a second.

They weren’t going to get anywhere standing here. Sans didn’t have any tools, any supplies, the machine needed to be repaired, _they needed to find the fucking S.E. core,_ and he couldn’t get any of that while he was here.

He didn’t know where he _could_ get it, but it definitely wasn’t here.

He allowed himself one more glance at Papyrus, and another at the machine.

Then he crossed the room on trembling legs and pushed open the door to the lab, into the unknown world outside.

He wasn’t sure why he was so cautious poking his head out. After that void, after that _nothing,_ he wasn’t sure if he could think of something worse. Besides, if Gaster really _had_ left, then at the very least he hadn’t died by simply leaving the lab. But still, Sans insisted on stepping outside before Papyrus, turning his head, scanning the landscape for anything out of the ordinary.

There was nothing.

Papyrus stepped out behind him, his eyes following Sans’s gaze, and Sans didn’t try to usher him back in.

“ARE WE … BACK HOME?” Papyrus asked, looking from side to side again, as if there might be some sort of obvious sign that would confirm it one way or another.

Sans’s mouth curled into the closest to a frown he was physically capable of. Even though all the other universes had looked so similar, he still found himself following his bro—Papyrus’s gaze, searching for anything to give him a hint of where they had ended up. There was none.

“i dunno,” he muttered. He glanced up at Papyrus, whose browbone had furrowed in something between confusion and distress. Sans huffed a sigh and started forward, away from the lab. “come on. we can’t stay here.”

He took a few steps, but paused when he didn’t hear Papyrus following him. He turned and met Papyrus’s wide, baffled eyes, his browbone furrowed even deeper, his arms held close to his body in a position so anxious Sans swore it was the same broken skeleton he had been failing to care for for more than a month.

“WHAT’S GOING ON, SANS?” he asked, and even though his voice was still booming, it somehow sounded quiet and unsure nonetheless. The tight line of his mouth trembled. “WHY DID HE WANT US TO GO IN THAT MACHINE WITH HIM? WHERE WAS HE TAKING US? WHY … I THOUGHT HE WAS YOUR FRIEND.”

Sans’s chest twisted and stung, but he forced down the old ache that really shouldn’t have been there after all this time. He knew Gaster was gone. He knew Gaster wasn’t his dad anymore. He told himself that, over and over again, but it didn’t make it hurt any less.

Papyrus frowned harder and stared at his feet.

“YOU CALLED HIM DAD. BUT OUR DAD’S …”

Sans tried to suppress the panicked jolt that ran through him. It didn’t work.

If Papyrus saw it, he gave no sign. He was far too focused on staring at the ground, shifting from foot to foot, wringing his hands, even with his gloves they were still _his hands,_ he moved them the same way, Sans was the one making him so upset maybe he had been happy before he had come here happy with his Sans happy with his own life happy without some stupid brother screwing it all up—

“HE DID SOMETHING BAD, DIDN’T HE?” Papyrus asked, furrowing his brow and tilting his head as he looked up at last. “HE SAID HE WORKED WITH YOU AT THE SENTRY STATION, BUT …”

He trailed off, and Sans clenched his teeth. He still couldn’t tell how much Gaster had actually learned about this Papyrus and how much Papyrus had filled in on his own. Either way, Papyrus had believed him. Believed another skeleton who he had never seen before in his life.

Had his Papyrus been so trusting?

Sans swallowed and looked away.

“we need to find him,” he muttered, as much to himself as to Papyrus, forcing all the other thoughts to the back of his mind. “he’s … he’s got something that i need to fix the machine. once i fix the machine, we can …”

“WE CAN GO HOME?” Papyrus filled in for him after he trailed off.

Sans didn’t say no. He couldn’t say yes. So he said nothing, and hoped that Papyrus would fill in the blanks on that, too.

Neither of them said anything else. Sans pushed the door to the lab shut and started off toward Hotland, the only way he could think of to go, and Papyrus followed close behind him.

It looked like Waterfall, in every way Sans could think of. And there were people there, not piles of dust. He didn’t recognize the individuals, but they seemed enough like the random monsters he had passed back in their universe.

The chances that they had landed in their own universe were minuscule—probably, it wasn’t like he had an exact number of how many universes there were in the first place. And most of the universes they had visited had seemed similar to theirs at first glance. But … he couldn’t see any major differences so far. Nothing out of place. Nothing obviously wrong.

It didn’t bring him the relief he might have expected. He still didn’t know where Gaster had gone. Hotland was a good place to start searching, but Hotland was still big, and if he wasn’t there … he could have gone on to the castle to try to get the rest of the souls. He could be in the Capital, and if he _was,_ there would be no finding him in that mess unless he caused enough trouble to draw attention to himself. And by the time he did that, it might be too late to do any good. Too late to do anything but follow Gaster back into the machine, back to their own universe or to any other universe Gaster wanted to go to first.

At least it would get them home. Maybe.

If that was their only option, if it was the only way to get Papyrus somewhere safe and _keep_ him there, if it was a choice between following Gaster and doing something stupid that got them stranded in a strange universe where he didn’t know a damn _thing_ …

He reached a corner and turned right, his eyes still locked on his feet.

And walked straight into someone scurrying the other way.

He fell back, stumbling into the ground so hard he swore he felt his HP go down—or maybe that was just the lack of sleep and food. He paused for a second, getting his bearings, trying to focus on Papyrus’s voice asking him if he was okay, as well as the yellow shape in front of him.

He paused.

The yellow shape he had bumped into.

The yellow shape that was moving.

The yellow shape that … squeaked, and stared at him from behind familiar glasses with wide, startled eyes.

“… alphys?” Sans breathed.

The yellow lizard monster shifted back a bit, eyes even larger than before.

“Oh! I-I’m so sorry, I-I didn’t s-see you there! Oh my god, you’re n-not hurt, are you?”

That was her voice. That was _Alphys’s_ voice. That was … that was the same voice he had heard since he was five years old, the same voice that made up some of his best childhood memories, working on his school assignments, collaborating on projects, talking over the phone because he couldn’t bring himself to look her in the eye—

But … this wasn’t Alphys.

Because Alphys didn’t wear a lab coat.

Her shock seemed to have settled a bit, and now she watched him with something closer to concern than anxiety over her own mistake.

“Um … a-are you okay?” she asked, tilting her head and pushing herself up to sit a bit straighter. She still had that hunch he was so familiar with, though it wasn’t quite as pronounced as he remembered.

Sans tried to talk, but he couldn’t stop staring at her, just like he couldn’t stop staring at the other him, the other Papyrus, the other—

This was her. Another version of her. Did that even count?

“HELLO!” Papyrus said, as cheerful as ever, snapping both Sans’s and Alphys’s attention up to him where he stood to the side. “I AM THE GREAT PAPYRUS! AND THIS IS MY BROTHER, SANS!”

“O-oh, um … I’m D-Dr. Alphys,” Alphys said, pushing herself to her feet on shaky legs. It took Sans several seconds to recognize exactly what was wrong with that introduction. Papyrus grabbed him under the arms and lifted him to his feet, and Sans came very close to falling over once again. Alphys turned her attention back to him, fiddling with her hands close to her torso. “You a-already knew my name, though. Have … h-have we met? You look f-familiar … d-didn’t I see you walking around in H-Hotland earlier?”

Sans kept staring for a few seconds after that, his voice still dead in his throat. He wanted to hug her, and at the same time he wanted to run as far away as he could get.

This was wrong. This was all wrong. It wasn’t her, it wasn’t his Alphys, he hadn’t seen her in over a month, but it looked like her, it sounded like her, she had the same stutter, the same nervous smile—

“uh … maybe. yeah, um,” he managed, forcing his mind back on some semblance of a clear track. He swallowed. “dr. alphys, you said?”

Alphys smiled wider. He hated the spark of joy that flashed through his chest at the pleased gleam in her eyes.

“Y-yeah! I-I work under the Royal S-Scientist.”

Sans’s browbone furrowed, and one by one, the words clicked, the flash of joy twisting into something that made him want to shudder and smile all at the same time. “you work in the science department?”

“S-sure! Uh-huh!” she replied. She paused, and her smile slipped, just a bit. “You … s-seem confused?”

“no. no,” he said, before he even had the chance to think. His smile curled up, and the urge to shudder slipped away as he looked at her, lab coat and name badge and _everything_ he had wished for her since they met. He smiled wider still. “you’re perfect there.”

Alphys blinked. “S-sorry?”

Sans flinched, and his smile fell. He cleared his throat.

“nothing.”

Alphys stared for a second longer, her brow furrowed, but finally, she nodded. “So, um … i-is there a-anything I can help you with?”

She looked to Papyrus, and Sans wanted to smack himself over the head with a brick for forgetting his brother was standing right there. He was so quiet … this Papyrus never seemed to stay quiet for long. But at the new attention, Papyrus’s baffled expression slipped, and he broke into a wide, eager grin.

“WELL, WE WERE WONDERING—”

“—we’re going to hotland, actually,” Sans cut him off, so fast he knew there was no way he could pass it off as casual. Both of them looked at him. Sans looked away and made a gesture that felt like a shrug. “there’s … someone we’re looking for, and i think he might be there.”

“O-oh!” Alphys smiled a little wider, something like hope in her eyes, the same hope that always appeared when she thought she could do something useful. “I was actually on m-my way there, t-too. We c-could … go together? I-if you want?”

Sans hesitated. But before he could even think of a response, Papyrus’s face had broken into a wide grin.

“THAT WOULD BE WONDERFUL,” he replied, with so much enthusiasm that Sans could almost forget everything he was trying to keep from him. “YOU SAID YOU WERE A SCIENTIST? MY BROTHER LOVES SCIENCE-Y STUFF! HE NEVER DOES ANYTHING WITH IT, BUT HE LOVES TO LOOK AT BOOKS ABOUT IT!”

“R-really?” Alphys asked, turning to Sans again, smiling a little wider. “T-that’s cool. I … I-I’ve got a lot of stuff I j-just look at in books, too.”

Papyrus hummed in agreement. “BOOKS ARE FUN. I HAVE A WHOLE SHELF OF BOOKS BACK HOME! BUT WE’RE VERY FAR AWAY FROM HOME NOW, SO I DON’T KNOW HOW I’M GOING TO GET IT BACK.”

He got a funny look on his face for a second, but it was gone before Sans had the chance to try and read it. Then he was marching ahead, past Dr. Alphys, in the direction she had come.

“COME ALONG, BROTHER, DR. ALPHYS, WE HAVE SCIENCE THINGS TO SEE.”

Sans felt his mouth twitching up at the corners despite himself. He wasn’t happy. He didn’t know how he could ever be happy again. But there was Papyrus, Papyrus who had seen things Sans couldn’t have imagined even a day ago, pressing ahead as if nothing was wrong.

It wasn’t much. But it was something.

Alphys stared between the two of them with wide, baffled eyes, settling at last on Sans with her brow raised in question. Sans bit back the sigh itching to make its way out of his throat, and glanced over his shoulder toward the lab, abandoned, vulnerable, and, at the moment, completely useless.

But hopefully not for long.

He straightened his head and followed Papyrus, Alphys trailing close at his side.


	47. Chapter 39

Papyrus kept the conversation going for the first five minutes of the trip, but after he found that Alphys wasn’t the most eager conversation partner, he let it fall back into silence. Sans had thought he would prefer things to be quiet, so he could think, but as soon as Papyrus stopped talking, Sans wished he would start up again.

Because that was just it. The silence let him _think._

And he didn’t want to think.

Even though he really, really needed to.

They were going to Hotland. That had seemed like a good idea when it first came to him, and it was still the only thing he could think of. But he didn’t know what he was going to do once he _got_ there. It wasn’t like he could just sneak off and hope to find all the parts he needed just lying around. He wasn’t even sure _what_ he needed. He would have to get to the lab, for one, and he sincerely doubted that Alphys would buy whatever excuse he came up with to wander off once he got there, and getting back _out_ with a bunch of stolen equipment … even if he could manage one of those steps, the chances that he would be able to manage all of them without drawing Alphys’s attention were slim to none.

He had no idea what he was going to do. He wasn’t even sure if Gaster had gone to Hotland. For all he knew, he could have gone on to the Capital. Sans didn’t know if Gaster had any way of getting to the human souls, if he even knew where they were kept, but … if he had come this far, Sans doubted he would give up easily.

He didn’t know how much time they had. And at this point, he wasn’t even sure he cared about stopping him.

He just wanted to go home. He just wanted both of them to go home.

Even if he had no idea what they were supposed to do once they got there.

His eyes drifted to his side, toward Alphys. Not his Alphys, but still _Alphys._ She dressed different, and she carried herself different, but the whole time he listened to her talking to Papyrus, all he could think about was all the ways in which they were exactly the same.

She was smart. Not that he had doubted that—but it was strange, talking to this Alphys and realizing she was just as smart as the one he had left behind, but she had actually _done_ something with it. She had followed the dream she used to go on and on about when they were kids. She could probably still be doing more, but at least she had _started._ At least she had … tried.

Everything he had been nudging her toward for years, ever since she graduated, had come true here.

In a world where he didn’t exist.

He tried not to think about whether his absence had anything to do with it.

He caught her fidgeting out of the corner of his eye, and turned just in time to see her glancing back and forth between him and Papyrus, her eyes wide with that curiosity that had never fully left.

“So are you guys from H-Hotland, or …?”

Before Sans could even think of responding, Papyrus perked up.

“SNOWDIN, ACTUALLY!”

“S-Snowdin?” Alphys repeated, smiling. “I hardly e-ever go t-there. Is it nice?”

Papyrus beamed.

“OH, IT’S WONDERFUL! IT’S VERY COLD, BUT I DON’T REALLY NOTICE IT SINCE I DON’T HAVE SKIN. AND THERE’S LOTS OF ICE CREAM EVERYWHERE TO BUILD SNOWPEOPLE WITH.”

“I-ice cream …?” Alphys asked, brow furrowed. But Papyrus had already gone back to looking around at the new scenery, and Alphys didn’t press him for more of an answer.

Sans glanced at his brother, taking a moment to really look at him for the first time since they had left the lab. His expression had changed. It was … Sans didn’t really have a word for it. Maybe “uncomfortable.” It wasn’t the same kind of “uncomfortable” that Sans was used to from his Papyrus. It was … muffled. Twisted. Even when his Papyrus had tried to muffle his own emotions, Sans could usually still make out the feeling underneath. This was just a general sense of discomfort, covered up with a tight, cheerful grin that Sans might have believed was real if he hadn’t been paying so much attention.

He looked away before Papyrus could notice him staring, turning back to Alphys and forcing his thoughts to follow. She had apparently forgotten the “ice cream” comment and was back to staring in front of her, fidgeting, her thoughts bouncing around in her head so hard Sans swore he could hear them hitting the insides of her skull.

Alphys was smart. But she was also trusting. Probably too trusting for her own good sometimes.

She knew when something was wrong. Maybe this wasn’t the same Alphys, but he knew he wouldn’t be able to fool her for long.

And if she was going to find out something was wrong anyway, he might as well use that to his advantage.

Besides, the idea of telling Alphys the truth—even if it was only a fraction of the truth—felt better than he wanted to admit.

He cleared his throat, and in the relative silence, it took less than a second for her to turn to face him again.

“so … you know a lot about mechanical stuff,” he said, and even though he tried as hard as he could to make himself sound casual, it was more than a little difficult when Alphys looked _so damn much_ like the one he remembered.

“H-huh?” she asked, blinking. Then the question seemed to hit her and she looked away, a faint flush on her cheeks. “W-well … some. I mean, I do all k-kinds of stuff at the lab, but y-yeah, I’ve always liked working with m-machines … w-why do you ask?”

Sans hesitated. He could feel Papyrus’s eyes on both of them, curious, unassuming. He didn’t look back to confirm it.

“i … actually have a machine i’ve been working on for a while. but it’s … broken. i don’t really have anything to fix it, and a second eye would be really helpful, especially since i only have one.”

Alphys turned to him again, brow furrowed. “W-what?”

Sans blinked.

Right. She didn’t know about him being half-blind. That was going to take some getting used to.

Sans cleared his throat again and shrugged.

“you know, it’s always good to see a second opinion.”

“O-oh, um … sure! I’d be h-happy to help!” Alphys replied, though now she seemed to be looking at a little more closely at his eyes. She wouldn’t see anything, of course. On the surface, his eyes were identical. But she had always been curious, and he had to fight back a fond smile at the sight. After a second, she seemed to realize her own behavior, and flushed again before turning to the path in front of them. “S-so what do you n-need to start?”

Sans hummed and shrugged.

“well, i need some tools. and i think some parts are kinda … beyond repair, so I’ll probably need some new ones.”

Alphys nodded, offering a slightly-less-nervous smile. “W-well, I m-might be able to h-help with that. We’ve g-got some parts for d-different kinds of stuff around the lab … i-if you want, you could s-see if anything would work for your machine?”

It was a small chance, and probably not a very good one at that. But despite her anxiety, Alphys carried an odd sort of reassurance he had never found in anyone else—or maybe she was just familiar. Either way, he found his bones relaxing, and his head tilting up and down in a nod.

“that sounds good,” he replied. “thank you.”

She smiled wider and stood up a little straighter than before, despite the deepening blush on her cheeks. “No p-problem.”

It wasn’t his Alphys. It wasn’t the same girl who had babysat him several times a week for years, the girl who had helped with his projects and supported him and invited him over on weekends to watch anime with her. But it was still Alphys. So he still found himself smiling back.

They turned ahead and kept on walking.

They talked a little more after that. Nothing long, nothing deep, nothing important. Just small talk, carefully avoiding any uncomfortable questions that would lead to answers Sans didn’t have. He tried to steer the conversation toward her, but just like his Alphys, she seemed to prefer to speak about just about anything else.

Like anime. He could really get her going if he asked her about anime.

At first, Sans thought Papyrus was too distracted looking around at the scenery of Waterfall—and soon, the edges of Hotland—to pay much attention to their conversation. But once or twice, he caught him watching them for just a second before he looked away again.

It wasn’t long enough for Sans to read his expression. He didn’t need to.

Sans tried to draw him into the conversation, once or twice. It worked for a minute, but this Papyrus and this Alphys didn’t have the same things to talk about as the ones in his universe had. They didn’t know each other, their likes and dislikes, the things they had in common that could be so hard to notice among all the other ways in which they differed. So for the most part, the rest of their trip was silent.

He found himself getting more nervous once the looming white lab building came into sight. He shouldn’t be nervous. This wasn’t his world’s lab. He had never been here before, there were no bad memories attached to this place, they were safe— _not safe never safe not while Gaster is here_ —no one was going to strap them down or try to hurt them. Chances were, without Gaster, this lab was actually being used for proper science.

Like it had been in his world.

For a while, at least.

Alphys swiped her key card—Sans couldn’t suppress the rush of joy at seeing Alphys with her _own key card_ —and stepped into the main area of the lab. It was bright, mostly white, with a few tables and chairs, sparse decorations, and piles of papers here and there. This had always been the communal area of the lab in his own world. Hardly anyone spent much time here, but it was where paperwork was placed before it was submitted to the king, and occasionally where scientists would meet visitors who weren’t inclined to go down through the lower labs.

It was a mess, but it was never as much of a mess as the one downstairs.

Alphys led them into the elevator, and Sans had to resist the urge to grab Papyrus’s hand—whether for comfort or to make sure that he didn’t get pulled away from him, he didn’t know. The elevator felt the same as his own: creaky, old, but for the most part, reliable. It took a minute to take them all the way down and jolted a little when it stopped, and when the doors open, for a second, it was all Sans could do to keep from smashing his finger into another button and taking them back up to the surface.

Not the same lab. Not the same lab.

Gaster wasn’t here.

Right?

Alphys stepped out, followed by Papyrus, and Sans forced himself to move before the doors closed on him. It was just as dim down here as it always was. Several of the lights seemed to be breaking, and maintenance didn’t come here often enough to fix them. But the more they walked, the more differences Sans could see.

The layout was different. Not much, but after they turned the corner and his eyes automatically searched for the familiar doors, he found almost none of them. Nothing obvious to the unfamiliar eye. But there were a few doors he was sure had been there before that were gone now, and one or two new he didn’t recognize. He was so distracted he didn’t even notice them passing by the lab that had been Gaster’s in his world, and almost ran into Papyrus before he realized they had stopped in front of Dr. Japer’s.

Not Dr. Japer’s.

Was it?

Alphys pushed the door open, and Sans fought back every urge to step back, to stop himself from seeing what was inside. Alphys was going in there, so it wasn’t Dr. Japer’s lab, right? She would have her own lab, if she worked here. Everyone did. But … maybe they didn’t here?

She stepped inside, and Papyrus followed, glancing over his shoulder to make sure Sans was right behind him. Alphys flicked a switch on the wall, flooding the room with bright, artificial light. Sans found his eyelights squinting, just for a second, as they adjusted.

It was Dr. Japer’s lab.

But at the same time, it definitely wasn’t.

It was the same room, without a doubt. But Dr. Japer had always been neat, almost uncomfortably so, and this lab, _Alphys’s_ lab … wasn’t. By any definition of the word. She made Gaster’s messiest days look like minimalism. There were posters hung over the walls from various anime, little figurines interspersed among the piles of paperwork, and the keyboard of her computer was barely visible under all the snack wrappings.

All in all, it reminded him a lot of Alphys’s house.

Alphys fidgeted some more as she stepped in further. A second later, she cleared her throat and gestured for them to come in.

“W-we can s-start looking here. T-t-there should be s-some scrap metal l-lying around … old p-parts … a-and tools, of c-course! W-whatever you n-need, let m-me know, and we can t-try to find it …”

Sans gave her what he hoped was a reassuring smile, before remembering that the smile had only worked on his Alphys because she had known him for so long. But still, this Alphys looked a little more relaxed upon receiving it, and gave him a smile in return, nodding as she stepped further into the lab.

“WOWIE,” Papyrus breathed, snapping Sans’s attention back to him. “THIS PLACE HAS A LOT OF WEIRD SCIENCE STUFF!”

It didn’t sound like a judgment, and Papyrus was looking around with a smile, confused but curious, so genuine Sans almost believed it was real. Sans jerked his gaze away before he could bring himself to appreciate it. It wasn’t the same. It would never be the same.

He needed to focus.

He started toward one of the first piles of apparent junk he found, already cataloging everything in his head and trying to figure out what the hell would actually be useful in repairing the machine.

“Alphys?”

The voice reached him mid-step, and Sans spun around so fast he almost fell over.

To face Gaster, standing in the open doorway, staring at them with wide, baffled eyes.

And for a second, just a split second, he was ready to summon one of his blasters right there and blast away the man he had once called his father, and half the lab with him.

Then he paused.

And he looked.

It was Gaster. It was definitely, without a doubt, Gaster. The same Gaster he had seen every day of his life. The same Gaster he had seen in that other universe, standing on the Surface with his two sons.

But it wasn’t.

Because Sans was quite sure that the Gaster he knew didn’t have two deep cracks running out from his eyesockets, one up his skull, the other down to his jaw.

And it had been a long, long time since he had seen that face watching him with such innocent, gentle curiosity.

And no matter how bad things had gotten, he was quite sure he had never seen him look at him like a stranger.

“O-oh!”

Sans jumped at the embarrassed squeak beside him, and turned just in time to see Alphys flash him a nervous smile before turning to Gaster again, holding out an arm as if to present an honored guest.

“Dr. G-Gaster, this is S-Sans. Sans, I-I’m sure you’ve heard of D-Dr. Gaster.”

“… yeah,” Sans murmured, barely louder than a breath.

Apparently it was loud enough for Gaster to hear him, though, even from across the room—or maybe he just hadn’t been waiting for a response. He took a step forward, offering a small, polite smile before lifting his hands in front of his torso.

SANS? GOOD MEET-YOU.

Sans nodded on reflex and offered what he hoped was a friendly hum, and Gaster nodded before turning back to Alphys and lifting his hands again. Alphys was saying something as well, but the words went right over Sans’s head.

Gaster was … signing.

He wasn’t even talking.

And he was _signing._

Sans had seen Gaster sign before, of course. He had signed around other people so often when he was growing up that it was inevitable that Sans and Papyrus would pick it up, and Sans had met enough nonverbal monsters at university for the language to solidify in his head.

But Gaster had never signed to _him._

His _dad_ had never signed to him.

He had never needed to.

He had been talking when he came in, but now that Sans remembered it, it had sounded … quiet, unsure. Unused. How long had it been since he had spoken aloud? How long had it been since he had had someone he could speak to? Someone who could actually understand him?

They didn’t exist here.

Sans had figured that out before, he had been almost certain, but this … this was unmistakable. Gaster was looking right at him, and Sans didn’t see even a flash of recognition in his eyes. Only interest. And confusion.

A lot of confusion.

He was staring, even though he did a fairly good job of hiding it.

It took a second for the obvious to click.

If he and Papyrus didn’t exist … then there were no other skeletons left. They had all died two thousand years ago, and Gaster had never completed the accidental experiment to create two more.

It was probably a wonder he hadn’t pinned them to the wall and demanded to know where they got off dressing up as dead people.

As it was, he just looked … startled.

Too startled, apparently, to act.

At least for the moment.

Alphys cleared her throat, and even though Sans was fairly sure she hadn’t been trying to get his attention, he still snapped his head up to look at her.

“S-Sans was w-wondering I-if … h-he has this m-machine he’s t-trying to fix …”

Gaster looked to her, then to Sans again, lifting his hands. NEED PARTS?

Sans couldn’t bring himself to speak. Alphys nodded in his place.

“W-well, y-yes … I-I think y-you wanted a s-second opinion, too, right?” she asked, turning to Sans with her brow raised, a slight smile on her lips. “D-Dr. Gaster’s the s-smartest person I k-know, h-he could—”

“don’t worry about it,” he cut her off. She stopped, staring. He turned to Gaster and did his best to make his smile look real. “just some parts would be great. and some tools.”

Gaster paused. SURE?

“yeah,” Sans managed, and even though his voice choked off in his throat, Gaster didn’t protest.

But instead of turning around and searching for whatever supplies he could find, his gaze drifted over Sans’s shoulder, and his mouth tilted up into a soft smile.

HELLO. NAME-YOU?

It was only as Sans turned around to follow the line of his eyes that he noticed Papyrus standing only a few feet behind him.

He had been there the whole time. He had walked behind them the whole way from Waterfall, the whole way through Hotland and into the lab.

And Sans had forgotten he was there.

Just for a minute.

Alphys hadn’t acknowledged him, or even introduced him. And Sans hadn’t protested, hadn’t stepped in to make sure he was included, even if he could blame it on shock.

And there was Gaster, smiling at Papyrus while Papyrus stared back at him, as if surprised that someone had actually noticed he was there.

Then, a second later, the shock morphed into a beaming grin.

“OH! HELLO! MY NAME IS PAPYRUS! SANS IS MY BROTHER!”

Gaster smiled a little wider and nodded. GOOD MEET-YOU, PAPYRUS. I GASTER.

He spelled it out, both his name and Papyrus’s, and it took a second for Sans’s mind to catch up with the fingerspelling. He must have finger spelled Sans’s name, too, he just hadn’t noticed.

Sans couldn’t remember the last time he had fingerspelled either of their names. He had given them name-signs before they were old enough to remember it, and anytime he needed to introduce them to someone else, they usually took over speaking after he told them that they were his sons. After that, he would teach the newcomer his sons’ name-signs, but usually made do with just pointing toward whichever one he was referring to. Now that Sans paid attention to it, the letters looked … odd on his hands. He had finger spelled plenty of things over the years, but their names just looked wrong.

It didn’t so much as faze Papyrus. He broke out in an even wider grin, reaching out to shake Gaster’s hand in a gesture that felt even stranger than the fingerspelling.

“THAT’S FUNNY!” he said, still smiling. “I KNOW SOMEONE ELSE WHO LOOKS JUST LIKE YOU! AND WITH THE SAME NAME! BUT HE ISN’T AS FRIENDLY.”

Gaster just stared at him, half his browbone raised. Sans cleared his throat.

“anyway, uh … you said you could help us get some parts?”

Gaster kept staring for a moment after that, then smiled, so convincingly that Sans almost believed him. But Sans knew that face, even if it had become almost unreadable at times over the past few months, even if this wasn’t _really_ the same face. And he knew when a smile on his dad’s face wasn’t real.

Nonetheless, Gaster turned to him and nodded.

OF COURSE.

It was only as he was pressed to actually find the parts that Sans realized he had no idea what he needed. Of course, there were the basic tools—he was fairly sure that the ones that were already in the room had come through along with the machine, but he hadn’t figured out the exact science of how the machine worked yet, so he wasn’t going to risk it. Besides, the tools he kept before were meant to _modify_ the machine, not make major repairs. He could use whatever help he could get.

He tried to focus on that, and only that, because that was all that mattered, getting out of here was all that mattered, it wasn’t any of his business what happened in this universe, it wouldn’t _change_ anything. But he couldn’t help his attention from drifting, to Papyrus standing nearby, somehow patient and fidgety all at once, and the other two people who had carefully slipped away while Sans was working.

They were far away—far enough away that normally, Sans wouldn’t have noticed the movement in the corner of his eye. But this wasn’t any sort of normal situation, and even with one bad eye Sans’s vision was still good enough to make out the signs all the way across the room.

It was more than good enough to make out the tiny creases on Gaster’s face.

WHERE FIND THEM? He asked, the motions slow and careful, as if he had been considering his words for a while.

Alphys bit her lip and shook her head, eyes falling to the ground like she did when she was embarrassed.

“I-I … I just b-bumped into t-them in W-Waterfall … w-why? I-is everything okay?”

Gaster shook his head, almost without missing a beat. Sans swore he saw his eyes flick to the two of them, squinting for just a second before turning to Alphys and offering another smile, even less convincing than the first.

EVERYTHING FINE. NEVERMIND.

It wasn’t fine, and Alphys knew that, just as well as Sans did, even if she didn’t know why.

A part of Sans wanted to stay as long as he could, to talk to this Gaster, to see what he did in this universe and if he was anything like _his_ Gaster and another small part of him wanted to scream at him for everything he hadn’t really done even though he had no control over it. But a much, much larger part of him just wanted to get away as fast as he could. So as soon as he had a bag packed with every sort of tool he could need for his project, as well as some wires and circuit boards and other parts that might, _might,_ be useful in repairing the damage, he started out of the lab, Alphys and Papyrus close behind him.

He didn’t turn to see Papyrus waving goodbye to other Gaster. He swore he could still see the other Gaster smiling and waving back.

It crossed Sans’s mind, just for a second, whether this was what his Gaster would have been like if he and Papyrus had never been born.

Then he looked at Papyrus, and he pushed that thought aside before it could show on his face.

None of them spoke for a long time after they left the lab. Even Papyrus had gone quiet, trailing behind them, looking around with an expression Sans could only describe as nervous, and a little bit uncomfortable. He wasn’t stupid. Even if he knew nothing about what was going on—even if neither Sans nor Gaster had taken the time to _tell_ him what was going on—he knew that none of this was right. He knew they didn’t belong here. Maybe somewhere deep down he knew that Sans wasn’t even the right Sans.

Sans tried not to think about the last one.

Instead, he turned to Alphys, watching her out of the corner of his eye as they walked side by side.

She must know something was wrong by know. She was brilliant—it was a miracle she hadn’t realized how very _wrong_ they were from the beginning. But even now, she said nothing about it. Sans wasn’t sure whether to be grateful or to wish that she and Papyrus would just _get it over with_ and call him out on everything now so he wouldn’t have to worry about it anymore.

He readjusted his grip on the bag slung over his shoulder. It was heavy, far heavier than anything he had lifted in a while, but his head was running in circles too fast for him to care about the strain in his bones. Alphys had offered to carry it, but he declined, if only because maybe carrying something would make him feel a little more productive, and distract him from the fact that he only needed to _be_ productive because he had destroyed everything in the first place.

He glanced over his shoulder at Papyrus. Still distracted. Still nervous. Sans couldn’t ignore that forever. At some point, very soon, he was going to have to talk about what had happened, even if he couldn’t give a full explanation—or tell the truth. He owed it to his brother. No matter what version of his brother it might be.

Finally, he turned to Alphys again, and tried five times to get words out before he finally managed a sound.

“where’d he get the cracks?”

Alphys jolted so hard she almost fell over, jerking around to face him with eyes wide and glasses crooked from moving so fast.

“W-what?”

“him,” Sans repeated, glancing back toward the lab, already a fair distance behind them. “the cracks on his face. where did they come from?”

Alphys stared. Sans felt another pair of eyes on him, silent, watching, but for once, paid them no mind. He waited as Alphys pulled herself together, starting off walking again at a somewhat normal pace. She fidgeted with her hands close to her torso.

“O-oh … I … well, I guess h-he never really made a public a-appearance right after … I-I thought everyone knew …” she murmured, apparently as much to herself as to him. She looked at him again, something like grief shining deep in her eyes. “He g-got them in the A-Accident.”

None of them spoke for several seconds. Sans’s browbone furrowed.

“the accident?”

Alphys nodded, but when his expression didn’t change, she tilted her head. “Y-you know … the Accident?”

She said it in the same way he might have talked about the barrier. The sort of thing that was so obvious, so well-known, even if most people rarely talked about it.

“what accident?” Sans asked, even though he already knew how strange the question must sound to her ears.

Her eyes widened, and she looked him over again, scanning him from head to toe, then turning to Papyrus and doing the same. Even Papyrus stiffened a little under her piercing gaze, and Sans was once again reminded that despite her anxiety, Alphys—at least, _his_ Alphys—had been sharp enough to notice one loose screw in the Core that was causing the whole thing to destabilize.

“A-are you … I t-thought you looked o-old enough to remember …” she started. Then she stiffened, looking away with a bright flush on her cheeks and rubbing the back of her head. “S-sorry, I …”

Sans waited without saying a word. He could feel Papyrus’s eyes on both of them. Part of him insisted that he shouldn’t talking about these things with his brother close enough to hear. But there was no way he could go back now.

Alphys cleared her throat.

“F-four years ago … when the C-Core exploded.”

For a few seconds, Sans wasn’t sure what he had heard. For a second, he thought that maybe the Core meant something else in this universe. Maybe the Core didn’t exist in the same way he knew. Maybe the Core was just a small machine in the lab.

But he didn’t need more than a few seconds to know how ridiculous that was.

He could see the Core, out in the distance, the same overwhelming machine that looked so small from this far away. And there was power, _abundant_ power, if what he had seen in the lab was anything to go by, the sort of power that wouldn’t be possible if the Core, or at least something like it, hadn’t been built.

And he could see the look on Alphys’s face.

The look that definitely wouldn’t have been there if she was talking about a small accident in the lab.

“the core … _what_? ” Sans breathed.

Alphys fidgeted more, tilting her head further to the side.

“Well, it didn’t _c-completely_ explode, it just …” She swallowed, glanced at him, then turned her gaze downward once again. “T-the metal on c-certain parts had o-overheated over time, apparently. It … Dr. G-Gaster tried to find a way to p-prevent it from being d-damaged, but one day it d-destabilized and p-parts f-fell in a-and …”

She was shaking. It was a faint movement, almost too small for him to see, but he had known Alphys for far too many years not to notice it—even from under an oversized lab coat. Her lips pursed and her eyes shone, and she squeezed them shut for a few seconds before opening them again and letting out a long, trembling breath.

“M-most of the m-monsters n-nearby had time to e-evacuate, but the people who w-worked there …”

She trailed off. Sans didn’t speak. Papyrus didn’t say a word. All Sans could make out was the sound of their breath and their footsteps, and faint hissing and rolling of the lava over the cliff nearby.

Alphys stared at the ground.

“I-I didn’t know them. I-I was … s-still in school t-then. I had m-met them once or t-twice, though, and … t-they were all nice,” she went on, and Sans could already hear the other words in her throat even before she said them. “Dr. Lemming was a g-guest lecturer at o-one of my classes … I’d … h-hoped to work w-with them someday.”

And now he could see them. All three of them. He could see their faces. Their smiles. Hear their voices echoing in his head.

He could see Dr. Lemming carrying their camera around everywhere they went, snapping photos of anything and everything, even if it didn’t seem important at the time. They were the one who had encouraged Papyrus in his scrapbooking, who had taught him the best techniques for getting the clearest photos, even if Papyrus still got too excited and snapped them without thinking about angles or composition or even whether the camera was focused. Their gentle warmth, their enthusiasm, even if they spent so much of their time by themself.

He could see Dr. Frewth, with all his snarky T-shirts and joke mugs and prank gifts that he hoarded away in his lab. The way he always seemed to know exactly how to make someone laugh, or even just smile, even if they punched him in the shoulder afterward for being so immature. The way he doted on every single one of his interns, like younger siblings or kids, buying them anything they liked, stocking the lab with their favorite snacks, and ensuring they had all the time off they needed, even if it meant he had to fill in for them.

And Dr. Japer …

His breath caught in his throat, and he bit back the noise that tried to force its way past his teeth.

Soft fur. Warm hugs. Gentle words. The sort of knowledge his dad had never been able to master, no matter how hard he tried.

He couldn’t even remember what her face looked like the last time he saw her. He had been far too focused on getting away.

Alphys fidgeted at his side, and when he turned, he swore he could see all three of them reflected in her eyes. People she hadn’t known, but had admired from a distance. People she would never know.

People who would have loved her, even if she didn’t follow the path they had expected.

“Dr. G-Gaster was the only one who m-made it o-out alive,” she finished at last, so quietly he could barely make it out. She lowered her head further. “T-that’s where he g-got the scars.”

Sans was very, very familiar with skeleton biology, but at that moment he would have tackled anyone who said he didn’t actually need to breathe. His body trembled even as he tried to keep it steady, and it was all he could do to keep walking and not trip over his own feet.

They were dead. His friends. His mentors. His _co-workers._

They had … they were … for _years,_ they had been …

But … that wasn’t them. It wasn’t … it wasn’t _really_ them, it wasn’t the _same_ them. _His_ Dr. Japer was still alive and well. And Dr. Lemming and Dr. Frewth. And his Alphys. They were all back home, waiting for him. All he had to do was fix the machine and get back to them and then everything would be alright, they weren’t dead there, the Core never exploded, the Core was _fine,_ they would all be _fine,_ they just—

They just had to fix the machine.

Sans breathed, and it hurt, but he kept going.

None of them said anything else the rest of the way to the lab. Alphys trailed a bit behind Sans once they got further into Waterfall, apparently realizing that she had no idea where they were going. Sans resisted the urge to wonder whether the path to the lab had changed with the universe and let his legs carry him on reflex. Apparently that, at least, had stayed the same, because after another ten minutes, he found himself staring at the same door he had left not two hours before.

He pulled it open more slowly than usual, poking his head in to make sure that Gaster hadn’t slipped back inside while they were gone. But the lab was just as empty as when they arrived, minus one broken-down machine that had stopped smoking and now just sat there, useless and ripped apart, in the center of the room.

He stepped inside, not bothering to turn around to see Alphys’s stunned face as she followed him, Papyrus right behind her. He could already hear her murmuring to herself, making observations, noting what would need to be replaced, what each part could be used for. If he closed his eyes, if he didn’t look at her lab coat, if he didn’t remember what they were doing here in the first place, he could pretend that it was his Alphys in the midst of another collaboration project, jumping right in despite her self-doubt, solving problems that had plagued him for weeks in a matter of minutes.

He took a deep breath and turned around, and thankfully, Alphys only took a second to notice his attention on her and turn to face him with wide, curious eyes.

“you sure you’re up for helping m—us?”

Alphys smiled, and it wasn’t his Alphys just like Papyrus wasn’t his Papyrus but he couldn’t help the softening in his chest as she shrugged.

“I-I don’t h-have anything to d-do today. And this looks r-really interesting. B-besides, t-this is really i-important for you guys, r-right?”

Sans swallowed against the lump in his throat and looked away. “… yeah. yeah, it is.”

He could see her nodding out of the corner of his eye. She didn’t say anything else.

Sans spent the next minute rifling through the items Alphys had packed for them, while Alphys laid out a few others on the counter—a counter that he hadn’t even noticed had made it through with the machine. How did that even work? There were drawers, too, had the things in the drawers come with them? If the machine could travel through universes because it was somehow permanent, a _constant,_ then …

He pulled open the first drawer on the left, feeling Alphys’s eyes locked on him but doing his best to ignore it. He wasn’t sure whether he had expected an empty drawer or not. He didn’t even remember what had been here in his universe. But right here, right now, he opened the drawer to find a set of folded-up blueprints.

Folded-up blueprints that he could recognize, even at a single glance, as the blueprints he had created himself for the modified machine.

He lifted them out as if they might crumble in his hands, nudging the drawer shut afterward. This was good. It was … confusing, but it was good. They could use these, especially if he was working with a partner. He tried not to think about how they had gotten here, exactly how all this worked. If the blueprints had come with him, had everything else come, too? His eyes flicked to the other drawers, the ones with his old lab badge, the ones with the photo album …

He clenched his teeth and shook his head.

Not now. He could think about this later. He could figure all this out later.

If he got the chance.

He set the bag next to the machine and the blueprints next to that. He started to reach for one of the tools, but found himself pausing and looking over his shoulder again.

Toward Papyrus.

He was right there, of course. He was always right there, he had always _been_ right there, it didn’t matter which Papyrus it was, he still stayed by his side. Following him wherever he went. Following him when he could have stayed home, could have stayed _safe,_ but of course that wouldn’t change a thing, of course that wouldn’t stop him from following Sans to make sure he was safe.

Even if he had no idea what was going on. Even if he was scared and confused and he didn’t know what Sans was doing or whether it would help him. Even if Sans ignored him. Even if the only people who paid attention to him were virtually strangers, even when Sans—no, it was _Gaster_ —who was the reason he might never get to see his real family again.

Sans wondered if the other version of himself even came close to deserving a brother as good as that.

He already knew _he_ didn’t.

Papyrus met his eyes, and as much as Sans wanted to look away, he forced himself not to. Papyrus’s mouth curled into a shaky, yet genuine smile, and he nodded toward the machine. Sans swallowed.

Then, with one last, long glance, he grabbed one of the tools from the bag, knelt down in front of the machine, and got to work.


	48. Chapter 40

**Notes for the Chapter:**

> Happy Valentine's Day! Here, have some sibling angst! (That's a traditional Valentine's gift, isn't it?)

There was no clock in the lab.

Had he ever installed one? He couldn’t remember. He had always found a way to remember to get out by five, for that brief time—how long ago had that been?—when he was working regular hours and remembering to come home for dinner with Papyrus. If there had ever been one, it was gone now. Or it hadn’t come along with the machine like the other things had.

It didn’t matter.

It had been a while, though. He was pretty sure of that.

Alphys helped a good deal at first, even though she had no idea what he was doing or how it worked. She had looked through the blueprints he had given her, while he worked from memory—he had the blueprints basically memorized. It had taken her only a minute to tap him on the shoulder and ask him how he had gotten these blueprints from Dr. Gaster, and whether he had been the one to create this machine in the first place.

Sans had no idea what she meant until he looked at the blueprints—for the first time in weeks—and saw them marked all over in Gaster’s illegible handwriting.

Apparently Alphys couldn’t understand his written font any better than most monsters, but she knew the symbols well enough to recognize them at first sight.

He brushed the question off, but he could feel her staring at him with wide, uncertain eyes for a good five minutes after that.

Still, she helped without much more complaint.

Papyrus, on the other hand, had no idea what was meant to be going on, and though he seemed to want to do something, he stayed off to the side instead, watching them, walking around, occasionally chatting with Alphys whenever she took a break. Sans hated seeing him in the corner of his eye but not hearing his voice. It was … wrong, Papyrus being so quiet.

He had been quiet for far too long already.

Sans worked. He repaired the parts that had been dented or damaged and replaced, to the best of his ability, the ones that had been broken beyond repair. He barely noticed when Alphys stopped handing him tools or asking him questions about where she should put what, or even looking at the blueprints. He wasn’t sure he heard her standing behind him.

He came very close to completely missing the careful, uncertain clearing of her throat.

“Sans.”

It would have been so easy for Sans to ignore her. He was focused, after all, and Papyrus had once told him that when he was focused on something important, he could probably sleep through a rock concert happening five feet from him.

But this was Alphys, and he couldn’t bring himself to ignore her voice. Not even when he found himself wondering, at least once every half-hour, whether he would ever hear his own Alphys again.

He turned around and found her wringing her hands, watching him with wide, concerned eyes.

“I-it’s getting l-late … are you s-sure you don’t want to stop for the night?” she asked, glancing down at the watch he hadn’t even noticed her wearing before.

Sans started to tell her that he needed to finish this, he couldn’t leave now, he had to figure this out, he had to find a way to get the machine working again. Then he stopped, and he looked at her. _Really_ looked at her.

Tired eyes blinking behind her glances. Hands fidgeting in that quiet, anxious tic she got every time she was overwhelmed by a situation but was too scared to speak up about it.

And Papyrus, still standing by the wall, looking at them.

He didn’t look tired, per se. Or … he did. Maybe not sleepy. But he looked … drained. Like that bubbling energy Sans had come home to earlier that same day—no, that was yesterday, wasn’t it, had they really been gone a day—had finally begun to fade.

They hadn’t slept all night. And they hadn’t eaten anything all day.

Food didn’t sound very appealing right now, not to Sans, and he wasn’t sure Papyrus would want to eat either.

But he certainly didn’t have much of a chance to do so here.

And the machine …

Sans could lie to himself all he liked, but it wasn’t going to be fixed tonight, no matter how hard he tried.

Alphys brought him parts, sure, and he had been able to repair quite a bit of the machine that he remembered. But that was the problem. He still didn’t know all of the changes that Gaster had made in secret. They were minor, changes he wouldn’t have noticed unless he had looked closely—changes he had almost completely missed during all that time working on it. Some of the changes were reflected in the blueprints—and Sans could read Gaster’s handwriting without any problem—but Gaster had never been very good about writing things down when he was in the midst of a particularly interesting experiment. So everything he had left out, Sans had to figure out for himself.

And no matter how much he managed to repair the machine itself, there was nothing he could do without the S.E. core.

Whatever the S.E. core had done to that machine, whatever it had made it capable of doing, nothing else could replicate it. And he couldn’t exactly make another one.

So he had to get it back from Gaster. Which would mean finding Gaster. Which … probably wasn’t going to happen right now.

He didn’t like the idea of stopping. He didn’t like the idea of leaving the machine unattended, especially since it would be far too easy for Gaster to sneak in here overnight and mess with it.

But what was he going to do with it? What would he _want_ to do with it? He had gotten ridiculous, completely irrational, but he wasn’t just going to sneak in here to break it. What use would that be? It was already plenty broken, and he must know that there was nothing Sans could do without the S.E. core. The most he could do was fix it, and that was what Sans was trying to do anyway, wasn’t it?

He might use it to go to another universe, then break it again so Sans couldn’t follow him, but … didn’t he seem intent on keeping Sans and Papyrus with him? Would he really be willing to trap them in another universe, maybe forever?

Sans didn’t know.

He didn’t know anything anymore.

But as much as he would have been willing to spend the night here, in this lab, he wasn’t going to do that to Papyrus, and he sincerely doubted Papyrus would go anywhere unless Sans came with him.

At last, he let out a long sigh and gave a slow, resigned nod.

“… yeah. sure.”

Alphys smiled, and Papyrus, standing by the wall now, looked up, his face unreadable.

“D-do you … n-need … where did y-you say you lived?” she asked.

Sans pushed himself to his feet, and only when his legs wobbled did he realize how long he must have been sitting there, crouched in front of the machine, straining his bones that were already far weaker than they had ever been before. He shifted a little, his gaze falling to the side.

“we’re, uh … on the hunt for a house right now actually.”

“YES, WE ARE ON THE HUNT FOR A HOUSE,” Papyrus piped in, and even though his booming voice made Alphys jump, Sans had never heard anything more welcome. Papyrus frowned. “ _OUR_ HOUSE. I LOOKED EVERYWHERE AND I COULDN’T FIND IT AND I DON’T THINK IT’S IN THIS PLACE EITHER. ”

Alphys stared at him for a few seconds, blinking, and Sans could practically hear the gears of her sharp mind just _trying_ to figure out what that meant. It was strange, watching an Alphys who didn’t know how to speak Papyrus. It was only as she cleared her throat and shook her head that he finally reminded himself that they weren’t five anymore, and this Alphys wasn’t his Alphys, and the memories he shared with her were his alone.

“Y-you can s-stay with me, if you want,” she offered, turning to Sans to flash him a smile before grinning up at Papyrus. “I-I’ve got a spare bedroom you can use, until you f-find somewhere more permanent.”

Sans hesitated. But it was a brief hesitation, and one he knew right away he wasn’t going to be able to stick to.

They couldn’t stay here. Or, well, _Papyrus_ couldn’t stay here. Sans wasn’t going to let him sleep in the lab, after all this. And Sans doubted they would find anyone else who would take them at such late notice.

“that’d be great, alphys,” he piped in, grinning back with a bit less effort than he expected. “thanks.”

Alphys beamed in return, and for a second, just a second, she was his Alphys once again.

“No p-problem!”

There wasn’t much to clean up. Sans wouldn’t have really cared if there _was_ a lot to clean up, given that there was so little reason to leave the lab clean in the first place. But as it was, there was hardly anything left out, if only because there had been so little in the lab to begin with, and there was only so much that he and Alphys could bring in here in the few hours since they had arrived.

He wasn’t sure whether the key would still work in this other universe, where he wasn’t even sure if there _had_ been a room like this before he had arrived, but when he pulled it out of his pocket and turned it in the lock, it clicked, and when he jiggled the handle, it refused to open.

It was pointless, almost certainly. He wasn’t stupid enough to think that Gaster hadn’t brought his own key with him.

But still. It made him feel better.

He flashed a glance at Papyrus as the three of them started back toward Hotland, and found himself wondering whether he had gotten so used to not seeing him over the past few weeks that he found it so easy to just … ignore his presence for all that time in the lab. He had been so quiet. Even quieter than _his_ Papyrus, and Sans got the feeling that this Papyrus was anything but quiet in his everyday life.

He couldn’t keep going on like this. Just … letting Papyrus trail behind him like a lost puppy. Even if it was the wrong Papyrus. Even if he didn’t get to keep him in the end. He had screwed up enough with his own brother. He couldn’t live with himself if he messed things up with this one, too.

More than he already had, that is.

But he didn’t know what to say. Especially right now, but he had hardly known what to say at dinner the day before, and he was afraid with every word that came out of his mouth that he was going to say something wrong, something that would tip this Papyrus off into realizing that _this_ Sans wasn’t _his_ Sans and then he would go looking for his Sans and Sans would be …

He didn’t want to think about it.

Not now.

Not yet.

So he walked at Alphys’s side, and Papyrus wandered along just behind them, looking around at the sights as if he hadn’t seen all of them just a few hours before.

They didn’t talk at first. Not Papyrus, not Sans, not Alphys. They just walked. Sans looked around them and took in the sights. Exactly the same as the ones he remembered. Everyone had already gone home for the evening, and if he didn’t look too closely at Alphys—didn’t glance behind him at Papyrus—he could almost pretend he was just heading home after a day of work with his brother and his best friend.

Then he looked at them, and the illusion shattered.

After the third of these incidents, he found his eyes focusing more and more on the white lab coat Alphys wore. She hadn’t taken it off since he had first run into her. It was odd seeing her in it, painful yet … relieving. Sort of.

He couldn’t remember how long he had wanted to see her in one. Even as a kid, when he tried on his dad’s lab coat, he insisted Alphys try it on, too.

For a second, he wondered if she had another, one he could snag and take home to his universe and give to his Alphys.

He stopped before he could remember that he still didn’t know how he was going to get back.

At last, he cleared his throat.

“so you work at the lab.”

Alphys jumped, like she had been startled out of a train of thought. Apparently even in a different universe, that part of her never changed.

She turned to him, blinking wide eyes as his words registered.

“Huh? O-oh … yeah.”

“you like it there?” he asked, unable to keep the affection out of his voice.

In under a second, her face lit up with a smile, her eyes all but gleaming with unbridled excitement.

“I l-love it! It’s … it’s incredible. I-I get to see s-so much cool stuff, and w-work with Dr. G-Gaster, he’s _brilliant,_ and I g-get to work on all these cool projects, it’s j-just … amazing.”

Her cheeks flushed, as if embarrassed by her outburst, but her smile didn’t fade. It was a different sort of smile than the one he had seen on her in his universe. Was this the sort of smile he had hoped to see on her, but never been able to imagine?

“you seem pretty comfortable there,” he replied, as casually as he could. “been there long?”

She glanced at him for a second before looking away with a shrug. “I, um … not very long, a-actually. J-just a few months. I … w-wasn’t going to before, but …”

She trailed off, and he swore he could see her cheeks beginning to flush again.

“but?” he asked.

Her cheeks went even darker. She cleared her throat, ducking her head as low as it would go.

“I … m-met someone. S-someone who … t-told me I should g-give it a try.”

Sans couldn’t remember how many times he had told her to “give it a try.” How many times had he suggested it and she just brushed him off? How many times had he nudged her toward the dream she had talked about since she was ten years old, only for her to change the subject like it didn’t matter?

“a friend?” he asked, and despite the jealous ache in his chest, his voice sounded just as soft.

Alphys jerked her head away, staring at the ground ahead of her, her cheeks almost bright red at this point.

“… Y-yeah. She’s … y-yeah,” she muttered, clearing her throat. She wrung her hands in front of her torso, ducking her head a bit further. “I always w-wanted to work in the lab, b-but I never t-thought I’d really give it a t-try, but then I-I met h-her and we t-talked and I-I told her how much I l-loved science and she s-started asking me w-why I didn’t work in the l-lab and I t-told her I was t-too nervous and she g-got all … well, she gets k-kind of _loud,_ b-but not in a mean w-way or anything, she’s just … t-that’s just how she talks, a-and she told me I-I should g-give it a try and a-at first I didn’t w-want to b-but she insisted and t-then she dragged me t-to the lab and it was r-really embarrassing b-because I w-wasn’t even d-dressed for an i-interview but she just m-marched right u-up to Dr. G-Gaster and told him he should h-hire me and h-he s-said he’d interview m-me the n-next day, I-I mean, it was r-really late, a-after normal w-work hours, but h-he stays late a lot, s-so I came back and w-we talked and I-I got the job and … well, t-that’s it.”

She cleared her throat again, louder this time, as if finally realizing what a lengthy ramble she had broken into. She glanced at him out of the corner of her eye, searching him for a reaction, and it wasn’t until then that he noticed the gentle smile on his face.

“she sounds great,” he replied, as genuinely as he could.

Alphys blinked, then smiled, more widely than he had seen her smile since he met her. This one, at least. She looked away, but she didn’t stop smiling.

“She is.”

“IT’S GOOD TO HAVE FRIENDS LIKE THAT,” Papyrus broke in, making Alphys jump. Sans turned to face him, walking just a step behind them, grinning an odd sort of grin Sans couldn’t put his finger on. “LOUD FRIENDS THAT MAKE YOU DO THINGS YOU WANT TO DO BUT DON’T KNOW YOU WANT TO DO BUT YOU DO THEM WHEN THEY SHOUT AT YOU ENOUGH TIMES.”

Sans’s furrowed his browbone as Alphys flashed Papyrus a shy, nervous smile.

There was something odd about the way he said it. But Sans was too tired to figure out why. So he let it go.

They walked for another five minutes after that. Alphys and Papyrus talked, and Sans kept his eyes ahead of him, mostly on the ground, letting his thoughts drift back to the machine and all the possible things he could do to fix it. It wasn’t a very long list. It was an almost nonexistent list, really, if he didn’t count all the more ridiculous ideas. He still didn’t know what all his resources were, maybe the dump would have something else he could use, but the thing that had made the machine work, the core, the _S.E._ core … he wouldn’t exactly find _that_ lying around in the dump.

Not unless another human fell into the dump.

And even then, he would have to …

“H-here we are!”

Sans looked up, and blinked at the sight he found ahead only twenty feet ahead of him.

It was Alphys’s house.

It was _his_ Alphys’s house, the same one she had lived in since she moved out when she was twenty-one.

He didn’t know how he hadn’t noticed the path here. Maybe because he had so rarely gone straight to her house from the lab. But this was her neighborhood, her home, and it was _exactly the same_ as it was in his universe.

His feet moved without conscious thought, following Alphys’s lead through the front door and into the mess that was her living room.

And it _was_ a mess. Not the same mess that he remembered, but Alphys’s messes had never been quite the same, and it had been months since he had been in her house anyway. It was still the same kind of mess. Anime DVDs and comic books and engineering reference textbooks and scrap paper filled with sketches of new ideas. He couldn’t be sure, but he thought there were a good deal more pieces of paper lying around here than he remembered.

He tried not to spend too much time looking at it. He didn’t want to consider the idea that he might never see his Alphys’s living room again.

He didn’t want to consider the fact that this was what Alphys’s living room looked like when she had followed her dream, and in his universe, he doubted she ever would.

Alphys had always had a spare room, even if she never used it. She didn’t seem to use it much here, either, and it was still a little dusty, but not overwhelmingly so. She offered them some food before bed—which they both declined—and told them that they were free to watch TV if they wanted, though Sans noticed her eyes drift toward her obvious anime collection a second later, her eyes glinting with anxiety, as if afraid that they would find some of her more embarrassing favorites.

Sans told her that they were tired, and were just going to try to get some sleep. He pretended not to notice how much it made her relax.

They didn’t bother turning on the lights when they got into the room. Sans wasn’t sure his eyes could take any more light. He just wanted to sleep. If he couldn’t work, he might as well get some rest, even if he couldn’t imagine making his mind quiet down. He just wanted to … stop thinking, whatever that meant, however he did it. He didn’t want to think about where he was, or who he was with. He just wanted to forget.

At least until he woke up tomorrow.

He didn’t want to think about how much damage Gaster might be able to do before then.

Sans shut the door behind them as Papyrus brushed the thin layer of dust off the bed and pulled back the old quilt, fluffing the pillows. It looked so much like his Papyrus that Sans forced himself to look away, shuffling around the room, pretending to look around. He couldn’t tell whether there were any differences between the room in this universe and the room in his. He had never paid that much attention.

Would he ever be able to check? Would he ever get the chance to see the room in _his_ Alphys’s house?

What if they couldn’t fix the machine? What if … what if they were stuck here? What if he never got to see his home again? What would Gaster do? Would he try to find a way to break the barrier in this universe? Or—

“YOU’VE MET HER BEFORE.”

Sans almost jumped, but after all the surprises he had had today, he found that he didn’t have enough energy to do even that. Still, he turned to face Papyrus, blinking, browbone furrowed.

“huh?”

“DR. ALPHYS,” Papyrus repeated. He wasn’t looking at Sans. He stared at a wall—specifically, at a poster of several anime characters giving peace signs. Just like before, Sans tried to read his face, but came up blank. “YOU’VE MET HER BEFORE, HAVEN’T YOU?”

Sans stared for a second, searching for an answer that made sense. “i …”

He trailed off. The answer was simple. Just tell him no. He had lied already, he had lied so many times, why the hell couldn’t he just lie again? He started to talk again, forcing the word, just _one damn word,_ past his teeth, but before he could get it out, Papyrus turned to face him, and he went silent again.

“YOU DON’T HAVE TO TELL ME IF YOU DON’T WANT TO,” Papyrus went on. He paused, then looked away. “I KNOW THERE ARE A LOT OF THINGS YOU DON’T LIKE TO TELL ME.”

Sans couldn’t even shake his head. He took a step forward, each movement shaky, his hand lifting from his side but not daring to touch him. “that’s not true, bro, i …”

His voice died one more time. Papyrus looked back at him, longer this time, and in the dark of the room, with the color of his extravagant clothes faded, it hurt how much he looked like Sans’s Papyrus. They had the same face, the same soft eyes, the same love and concern and care and this Papyrus had loved his Sans this much and Gaster had _taken them away from each other._

“YOU’RE A GOOD BROTHER,” Papyrus went on. Sans wanted to die. Papyrus’s mouth twitched at the corners, tilting into a sad smile. “YOU’RE A LAZYBONES AND YOU EAT TOO MUCH JUNK FOOD BUT YOU’RE A VERY GOOD BROTHER.”

Sans swallowed. Papyrus’s eyes softened further, and his smile slipped away.

“I WANT TO BE A GOOD BROTHER FOR YOU, TOO.”

“you are,” Sans cut in, and this time he didn’t even have to think. He shook his head. “god, you’re … you’re the best brother. you’re the greatest. the great papyrus.”

“THE GREAT PAPYRUS?” Papyrus asked, browbone furrowed.

Sans came far too close to saying that of course he was the Great Papyrus, Sans had said it before, maybe he hadn’t said it that many times but—

Then he remembered.

And he swallowed his words and forced a nod.

“yeah. that’s you.”

“THE GREAT PAPYRUS,” Papyrus repeated, as if testing the words on his teeth. He tilted his head. “I’M GREAT.”

It sounded far too much like a question. Sans swallowed again and widened his grin.

“you are,” he replied, barely louder than a breath. “better than i could ever be.”

Papyrus gave him a funny look, and Sans couldn’t tell whether or not he had heard what he said. He didn’t ask about it, but he also didn’t look away.

“WHAT HAPPENED?”

Sans stiffened. “what?”

Papyrus paused again, and this time he turned to face Sans in full, his head tilted to the side and his browbone creased even deeper than before.

“YOU’VE BEEN ACTING DIFFERENT. EVER SINCE … WE GOT TO YOUR FRIEND’S HOUSE,” he said. Sans looked down, but he could still feel his brother’s eyes on him, boring into him, deeper than they had in a long time. “HE’S NOT REALLY YOUR FRIEND, THOUGH. HE … TRIED TO HURT YOU.”

Sans didn’t even bother trying to refute him. There was no point now. Papyrus wasn’t stupid, and Sans was tired of trying to lie to him anyway, especially about something as obvious as this.

Papyrus waited, but when Sans didn’t respond, he dropped his gaze to the floor, holding his arms in a loose self-hug.

“I’M CONFUSED, SANS,” he murmured, his voice higher-pitched than normal, like a faint whine that somehow still sounded louder than Sans remembered. “I DON’T KNOW WHAT’S GOING ON AND I KNOW YOU DON’T WANT TO TELL ME BUT I DON’T UNDERSTAND ANY OF THIS I DON’T UNDERSTAND WHY YOUR FRIEND WOULD TRY TO HURT YOU AND WHY YOU WOULD TRY TO HURT YOUR FRIEND AND WHY WE GOT IN THAT WEIRD MACHINE AND WENT TO ALL THOSE PLACES THAT LOOKED LIKE HERE BUT THEY _WEREN’T_ HERE AND THEN YOU KEPT TALKING TO PEOPLE LIKE YOU KNEW WHAT WAS GOING ON BUT YOU NEVER TOLD ME ANYTHING AND … AND …”

Sans’s chest twisted as Papyrus drew a shuddering breath, shaking his head before lifting it again, meeting Sans’s eyes with his own sockets, brimming with tears.

“WHY WERE WE AT HIS HOUSE, SANS? HOW DID WE GET THERE? WHY DON’T I REMEMBER ANY OF IT? WHERE’S UNDYNE? W-WHERE’S …”

His voice broke, and suddenly Sans didn’t care that they were in another universe and he had no idea what they were going to do and this wasn’t even the same brother he had grown up with. This was his brother, and he found himself moving forward, arms outstretched.

“hey, hey, it’s okay, we’re okay, everything’s gonna be fine …”

It wasn’t fine. He didn’t know if anything was ever going to be fine again but he didn’t care. His brother needed him his brother shouldn’t have to deal with this he shouldn’t have gotten involved in the first place none of this was his fault and he didn’t deserve to hurt and _Sans kept hurting him—_

“YOU ALWAYS SAY THAT,” Papyrus cut into his thoughts, before his fingers could even brush his arms. He stared down at him, and he was still so much taller than him but he looked so damn young, scared and confused and infinitely trusting. “EVEN WHEN THINGS ARE BAD, YOU ALWAYS SAY THAT.”

“and was it a lie?” Sans asked.

As soon as it left his mouth, he regretted it. Because how many times had it been a lie? How many times had he avoided the truth with his brother just so he wouldn’t have to deal with the consequences?

But Papyrus’s face softened, the remaining tears still glistening around his eyes.

“NO. IT NEVER WAS,” he replied, almost as quiet as before. “IT WAS ALWAYS OKAY. BECAUSE … WE WERE TOGETHER. AND WE GOT OUT OF IT.”

It felt wrong, and staring up at him now, Sans knew it wasn’t that simple. But he still forced himself to smile and nod and stare up at his brother with ten times as much reassurance as he actually felt.

“and we’re gonna get out of this, yeah? it’s gonna be okay. we’re gonna be fine. we just need to …”

Yet again, he trailed off, the words dying in his throat. They just needed to what? What the hell was he supposed to do to fix this? It didn’t matter how much he loved his brother, it didn’t matter how determined he was, without a _way_ to get out of this, how could he …?

This time, it was Papyrus who stepped toward him, resting a gentle, careful hand on his arm. Sans barely held back a flinch.

“YOU LOOK SAD, SANS,” Papyrus said, and now Sans felt like the younger one, broken and vulnerable and afraid and it was so damn hard not to throw himself into his brother’s arms and just hang on. But he didn’t, and Papyrus just kept staring down at him, a thick crease between his eyes. “SOMETHING BAD HAPPENED BEFORE WE WENT TO YOUR FRIEND’S HOUSE. DIDN’T IT?”

Sans’s gaze dropped to the floor. He forced his hands not to curl into fists and blinked away the burning in his sockets. Not now. _Not right now._

“… yeah.”

“WHAT HAPPENED?” Papyrus asked, squeezing his arm a little tighter.

Sans’s bones trembled, so hard he almost fell over. Papyrus’s grip held him up.

“… something … i … i lost someone,” he murmured. “someone who … meant a lot to me.”

Papyrus paused.

“ONE OF YOUR FRIENDS?”

Sans choked on the air that slipped back his teeth. It sounded like a laugh and a sob all at once. Papyrus’s hand squeezed tighter.

“yeah. one of my friends.” His bones were almost rattling now. “a really good friend.”

Another pause.

“DO I KNOW THEM?”

It took so much effort not to laugh that Sans found himself almost choking again.

“not really,” he said, and he didn’t even know if it counted as a lie.

Silence. The room was so dark, so empty, yet just the sounds of their breathing felt like a storm. Like the rain pouring down from dark gray clouds, like the rain he could still hear echoing in his head, the rain and the laughter of his dad and his brother and himself, the ones he would never see again, but he swore he could still see them every time he closed his eyes.

“HAVE YOU TRIED TO FIND THEM?”

Sans blinked, and tilted his head back up to meet his brother’s gaze. “huh?”

“IF YOU LOST THEM … DID YOU TRY TO FIND THEM?” Papyrus asked, as if it were the most obvious thing in the world.

Sans stared for a second longer as the words processed, one by one. Then he ran his own words over in his head, and it was all he could do to keep from gawking. He looked down again.

“i … sort of. yes. and … and no.”

“WELL, YOU SHOULD TRY HARDER,” Papyrus said, without missing a beat, and even though it sounded strict, in a way, Sans had also never heard anything that sounded so kind. “THAT’S WHAT WE’LL DO ONCE WE GET BACK TO … WHERE WE WERE BEFORE. HOME. WHEN WE GET BACK HOME. WE’LL LOOK FOR YOUR FRIEND. TOGETHER.”

Everything hurt. His bones and his skull and his soul and his burning eyes that weren’t going to cry one more damn tear. He had changed his clothes—or some of them, anyway—but he swore he could still feel his brother’s dust on his shirt, covering his legs, seeping through his fingers, but he was here, he was _alive,_ he was talking to him but it wasn’t him, it would never be him he would never see him again even if he got out of here even if he got back home he would never see his brother again he was dead dead gone gone _gone_ —

“yeah, pap. that sounds good,” he managed, his voice barely slipping around the lump in his throat. He swallowed, but it only grew larger still. “we can … do that tomorrow.”

Papyrus’s hand lingered on his shoulder for a few seconds longer, then slipped away, falling back to his side. Half a minute later, Sans dared to look up, only to find Papyrus staring at the floor between them.

“I WISH YOU DID THIS MORE. TOLD ME THINGS,” he said, and even though it was still that loud, booming tone, it barely felt louder than a whisper. “I WISH YOU’D LET ME HELP YOU.”

Sans didn’t even try to find anything to say. The tears lingering in the insides of his sockets faded away, and he found himself as empty as the room around them.

Papyrus took off his shoes, set them carefully by the wall, and slipped into the bed on the far left side. He even laid down the same way as Sans’s brother had. How many little things would have stayed the same, and how many things would have changed? _Why_ had they changed? Would Sans ever even know? Or would all the little quirks of his Papyrus and this Papyrus blend together until he forgot what his Papyrus had been like in the first place?

He gritted his teeth, but jerked his eyes away. Not now. Not yet.

Later.

When this all was fixed, he could figure out what the hell was going to happen next.

He kicked his shoes off, letting them fall to the ground just beside the bed. Then he pulled off his jacket. He almost tossed it to the end of the bed, but on a whim, he pulled it close to him, and once he had settled down under the covers, he hugged it against his chest like he might hold a stuffed monster.

His head slipped down so he was breathing in right against the fabric.

It smelled warm, vaguely spicy, with a strong hint of sugar and chocolate.

It smelled like Dr. Japer.

He closed his eyes. But before he could even begin to drift into sleep, he felt a hand rest on his skull, bony fingers stroking over it in rhythmic patterns. Little circles, up and down, gentle and light. Then they pressed a little harder, rubbing his head with the practiced care he might expect of someone who had done it a thousand times before.

Had Dr. Japer still been alive, when this Papyrus was born?

Had she stayed around when they were infants? Had she come over to help that Gaster care for them?

Had she sat him in her lap and rubbed his head while she hummed a lullaby, until both brothers found themselves doing the same for each other on bad days, so instinctual they didn’t even know where they had learned it until Gaster told them?

If their Gaster was dead, had he been around long enough to tell them?

There were a thousand possibilities, a thousand questions he might never get the answers to. He didn’t know. And right now, lying here, next to his brother, he didn’t care. All he could feel was the familiar, smooth texture of the fingers against his skull, and if he kept his eyes closed, he could pretend that it was his Papyrus there in front of him, giving him a gentle, reassuring smile, no matter how much it hurt.

If this Papyrus was here, even if it wasn’t _his_ Papyrus …

At least he could pretend that he hadn’t lost everything.

He needed him. He had lost everything else. He couldn’t lose his brother, too. Not this one. Not again.

Sans allowed himself to shift a little closer on the mattress. After a minute, Papyrus’s hand stilled, but remained on his head, resting loosely over his skull. The rest of the world faded away, until all he could feel was the thrum of his brother’s soul, warm and alive next to his.

And right here, right now, it was all he needed.

* 

Sans was dreaming about high-pitched squealing.

It was a funny thing to dream about, and not a very good one. He had never dreamed about high-pitched squealing before. He didn’t like it. It made his head hurt, and he didn’t know how to make it stop. It sounded like something he had heard, though he couldn’t figure out where. Maybe the alarm on one of the machines in the lab? When the monitor measuring his vitals had gone off during the failed eye surgery? He had passed out right after that, he couldn’t remember much of it. The alarm when the human had escaped? He had hardly noticed it, he was too busy running down the hall, faster, faster, have to get to Pap, Pap’s in danger, the human’s out and something’s wrong and—

This was louder. Much louder. And much further away.

But he couldn’t figure out what it was.

Then the mattress jolted at his side, and Sans’s eyes opened to see Papyrus sitting up beside him, looking around the room.

Sans was pushing the covers off before he could think of it, jumping off the bed so fast he almost tripped over his own feet. He could hear the sheets rustling behind him, the thud of Papyrus’s own feet hitting the floor.

"SANS? WHAT’S WRONG?” Papyrus asked, booming yet somehow timid. “WHAT’S THAT NOISE?”

But Sans didn’t look at him. His eyes were on the window, the view mostly blocked from the buildings nearby but letting him see the faint flashing of a red light in the distance. Far in the distance.

He had heard that alarm before. He had seen that red light before.

Granted, he had seen a _lot_ of red lights before, and heard even more alarms, but this red one …

“stay here, papyrus,” he said, shoving on his shoes without bothering to tie them again. He scrambled across the room toward the door, pausing only when his hand touched the knob to look at his brother. “i’m gonna go see what’s wrong.”

Papyrus stared back at him, wide-eyed, for only a second before he started around the bed, toward Sans.

“I’M COMING WITH YOU.”

“no!” Papyrus stopped. Sans gritted his teeth, took a deep breath, and shook his head. “no, just … i’ll be right back. everything’s fine, i just …”

He trailed off.

He just _what_?

An alarm was blazing, a light was flashing, and he had no idea what the hell was going on.

But something was wrong.

Something was _very_ wrong.

And he couldn’t let Papyrus … not this Papyrus, not _another_ Papyrus …

He couldn’t risk it. Not again.

Yet even as he pulled the door open and stepped outside, he couldn’t help but wonder how much of all of this could have been prevented if he had told Papyrus the truth from the beginning instead of keeping him in the dark until it was too late.

Which was probably the only reason why he didn’t say anything when Papyrus strode out of the room behind him.

The house was dark, and as hard as he listened—as much as he tried to block out the muffled sound of the alarm—he could make out no hint of Alphys. Was she already up and out of bed? If this was so important, wouldn’t she have woken them up, too? An alarm that loud was meant to get everyone’s attention, and anything that was meant to get everyone’s attention was meant to make everyone _act._

He pushed the front door open—already unlocked, when he was sure she had locked it when she came back inside—and didn’t comment when Papyrus stepped out at his side. The streets were packed with people, older monsters, kids, a few faces he recognized, plenty he didn’t. All of them chatting at once, too many of them for Sans to pick out what anyone said.

But he didn’t need to.

As his eyes turned toward the noise, the noise everyone else was running _away_ from, Sans remembered where he had heard the alarm.

Not for real. Not for more than a few seconds, a brief test to ensure that if there _was_ a problem, if anything went out of the normal ranges, that the underground would know. That they would have every opportunity to evacuate if they were close by. That there would never be a major accident with casualties outside of the building—the sort of accident Sans had never really considered, but the sort of accident that had already become far too real here.

The alarm was coming from the Core.


	49. Chapter 41

**Notes for the Chapter:**

> I think this is a good day to say a tremendous thank you again to the person who inspired this story in the first place - and is also an incredibly amazing friend. Happy one-year friendversary, [Cat](http://archiveofourown.org/users/Randomcat1832/pseuds/Randomcat1832). :)

Papyrus was following him.

Sans had known he would, there was no stopping him, he _knew_ that, but that didn’t stop him from calling over his shoulder every minute or so, insisting that Papyrus go back to Alphys’s house, everything was fine, he just needed to check something.

But Papyrus wasn’t stupid. Sans knew that, even if the rest of the world sometimes couldn’t see it.

Sans could lie to him about some things and he wouldn’t even bat an eye.

But this time, he knew. He knew far too well.

So he kept following. And Sans, despite his better judgment, kept running forward, toward the alarm.

Toward the Core.

The alarm had been loud from the house, but now it was almost deafening. Sans didn’t even know that the Core _could_ be so loud. Was it that loud in his universe? He would have remembered it for sure, had his dad installed something even louder and just never mentioned it?

Or had they only installed it here after …?

Papyrus trailed just a bit behind him, not because he couldn’t run much faster with his long legs, but likely because he didn’t know where he was supposed to go. Of course he wouldn’t know. Aside from the alarm, at least. Had this Papyrus even _been_ to the Core?

If his dad had died when they were so young … did the Core even exist?

After a few minutes, he stopped telling Papyrus not to follow him, as badly as he wanted to. Maybe because he couldn’t get the words out, maybe because he didn’t want to slow down and waste any time, maybe because after all he had put him through he didn’t think he could bear barking out any more orders that sounded so harsh when his brother was just trying to help. So he stayed silent and focused all his energy in running.

For the second time in less than twenty-four hours, he only saw the yellow shape in front of him a second before he collided with it.

But this time, at least, he didn’t knock both of them over.

He stumbled, and so did she, both of them blinking and staring as they stepped back and stared at apparently the last person they had expected to see.

“alphys,” Sans breathed, though even as he said it, he found himself wondering how he hadn’t expected to run into her since she wasn’t at the house.

“S-Sans?” she asked, except her confusion was far more warranted. She glanced at Papyrus over his shoulder. “I thought y-you two were—”

“what’s going on?” he cut in. “what’s wrong with the core?”

Alphys paused, her mouth still hanging open, as if she hadn’t realized he had been talking. She clamped it shut a second later.

“T-the Core? It’s …” She trailed off. Then she tilted her head. “H-how did you know that alarm was for the C-Core?”

Sans froze. Then his mind kicked back into gear and he shrugged as well as he could with how badly his bones ached.

“well, it’s kinda loud. and the core’s big. seems logical.”

Alphys’s brow furrowed. Her eyes drifted toward the alarm, then back to Sans.

“I-I guess …” she muttered. She knew he wasn’t telling the truth. Not the whole truth, anyway. She had never taken his lies easily, apparently not even in a universe where she hadn’t had years to learn to tell them apart from the truth. But she shook off any other questions she had and took another step forward, toward the Core. “I … I’m just g-going to find out … y-you t-two can go back to the h-house, it’s f-fine, it’ll be—”

“i’m coming with you,” Sans cut in. Alphys’s mouth hung open for a few seconds before she snapped it shut. She seemed to struggle for her words, opening and closing her mouth a couple of more times. Before she could get out a single word, Sans heard the telltale sign of Papyrus’s footsteps coming up to stand at his left side.

“SO AM I.”

Sans’s head snapped to face him, and even though his mouth couldn’t technically open, he swore he felt it doing a very accurate impression of Alphys. His head was already shaking before he could even recognize how tall Papyrus was standing, how firmly his jaw was set, how his eyes burned with more determination than Sans had ever seen.

“papyrus, please. you …”

“I KNOW YOU THINK I CAN’T DO ANY OF THIS, SANS,” Papyrus said, and somehow, even with his booming tone, he still sounded quiet. His gaze locked on Sans for a few seconds longer before it fell to the ground. His mouth set tighter. “MAYBE I DON’T KNOW WHAT’S GOING ON OR WHY YOU’RE ACTING SO DIFFERENT OR WHY YOU SUDDENLY KNOW ABOUT ALL THIS SCIENCE STUFF BUT YOU’RE MY BROTHER AND THAT LOOKS DANGEROUS AND IF YOU’RE GOING, I’M GOING WITH YOU.”

He met Sans’s eyes again, and as much as Sans wanted to look away, as much as he wanted to escape those burning eyes, he couldn’t.

It was so easy to forget that this wasn’t his Papyrus.

It was so easy to look at this Papyrus and feel the ache of everything he had kept from his own brother, everything he could have done better. Every way that he had failed him.

It was Alphys who finally cleared her throat, drawing both of their eyes back to her, though her own were locked on the lab in the distance. She swallowed and shook her head.

“L-look, we h-have to hurry, I-I need to g-get there and s-see what’s …”

She trailed off, her teeth coming out to bite her lip. Her brow furrowed.

“I don’t understand, Dr. G-Gaster should be d-doing something by now …” she murmured, more to herself than to them. She glanced at them again, biting down on her lip so hard it was a wonder she didn’t split it in two. Then she made a quiet noise that sounded like a whine and threw herself forward, running as fast as her short, stubby legs could manage, Sans and Papyrus trailing close behind her.

And together, they ran.

Sans could almost believe that it was his Hotland they were running through. It looked the same, _exactly_ the same. And it might have been years since he had spent time with Papyrus and Alphys together, but it _had_ happened, it was just like the old days when she would come over even though she wasn’t getting paid to babysit and spend hours playing with both of them, running around the house and that was all they were doing now, running around, there was nothing wrong, maybe they were going to visit his dad at the Core, the Core looked the same, too, looming and overwhelming and magnificent, his _dad_ had made that and he couldn’t be more proud to say it—

Something hit his foot, and for several seconds he struggled not to fall flat on his face. A hand grabbed his shoulder, righting him, and Sans gave only a glance to Papyrus at his left before he looked to his right, where he swore he caught a flash of white scurrying off into the distance.

Was that a … dog?

He shook his head, brushing it aside, and started running again, Papyrus close at his side.

They made their way through the entrance to the Core, passing several panicked employees that Alphys immediately told to go home, get out of here, get to safety, she would fix this, she would find a way to fix this. She didn’t sound remotely confident, and Sans could see, even with a glance, that they didn’t believe her. He didn’t look back to check whether they did as she said.

She slowed once they were further inside, her feet stumbling like they didn’t know how to walk anymore, shifting her weight from side to side as she turned her head and scanned the different passages around them. It was warm here, burning, and even though it didn’t bother him, Sans could see Alphys sweating. She had never minded heat, and from the way she chewed her bottom lip, he doubted the temperature had anything to do with the moisture on her face.

“U-um … I d-don’t know w-where …”

She stiffened, then turned at them, blinking, as if she had forgotten they were there. She shrunk into herself before setting her face and straightening up. She was terrified, and very bad at hiding it, her body shaking harder than Sans had ever seen. But she had also never looked so tall.

“C-come on,” she continued, glancing ahead of her and pointing toward what appeared to be a random path. “M-maybe it’s t-this way.”

Sans knew the Core like the back of his hand—at least, he knew _his_ version of the Core. But he didn’t have time to figure out how much they differed, and even if Alphys didn’t look more than marginally sure of her own decision, it wasn’t like he had a better alternative. He followed her, and Papyrus followed him.

The first thing he noticed, in the back of his mind, was that there were no guard rails here. At least, there weren’t very many. There were a couple of spots where they had been installed, but there were far more spots where the platforms and the catwalks simply hung over the lava below. It seemed so trivial now, but that had been so important in his world, from the very first time Gaster brought them to visit the Core, he made sure that there were guard rails—or else he wouldn’t let go of their hands for so much as a second.

But they didn’t exist in this world.

Would Gaster have found another reason to install guard rails? Would _anyone_? It seemed so obvious, but if Gaster had made the Core, if he hadn’t had a reason to think about it …

He shook the thoughts out of his head and kept walking.

He tried to think of what Gaster could be doing here. Because this _was_ Gaster. It had to be, there was no way it _couldn’t_ be related to him when it had happened so suddenly, and in the _Core_ of all places. But why would he want to go here? He wanted the souls, didn’t he? And the souls wouldn’t be here. They would be in the castle. He should be in the _castle,_ or even in the lab, surely he had his own key, he could get in the lab and fix the machine, Sans was wasting his time here, it didn’t make any sense for Gaster to be doing this but _there was no other explanation._

The alarm was louder now, it must have been, yet it still faded into the background the longer they walked. He looked into every hall they passed, searching for anything out of the ordinary, he didn’t _know_ this place, it was the same but it was different and he didn’t know what was _supposed_ to be different and what had been changed, maybe this _was_ a coincidence, maybe he was just paranoid, maybe Gaster had already grabbed the souls and gone back to the lab and just set off something in the Core to keep Sans distracted.

Sans barely noticed his own footsteps slowing, letting him fall several steps behind Papyrus and Alphys as his mind wandered and his breathing sped up and his soul stuttered with the imaginary weight crushing him from the inside out.

Then something grabbed his hood and yanked him into the gap between two of the machines.

And Sans snapped out of his own head just in time to feel himself slam into the wall.

The metal was hot, burning, it probably would have left actual burns if he hadn’t been made of solid bone. Sans blinked, dizzy, before gathering his magic and getting ready to fire it off in a bone, even one of those blasters, he might as well use them for _something._

He looked forward, straight into the eyes of his attacker.

And he stopped.

As his own two eyesockets stared back at him.

His own two eyesockets, attached to his own skull, wearing a pale gray hoodie and staring at him with an expression Sans couldn’t read, even on his own face.

Sans blinked. The other him didn’t. Okay, so not a reflection, then. Probably. Hallucination? Maybe the Core had started emitting some weird gas and it was getting into his head. Or …

… there wasn’t another Sans in this universe, was there? One Alphys didn’t know? One _Gaster_ didn’t know?

He stared at the other him, and the other him stared back, stoic. Sans blinked again. The other him still didn’t. Sans adjusted himself against the wall, and the other him let go of his shoulder, stepping back just enough to put a bit of space between them, but not enough to allow Sans to slip away without being intercepted. Sans rolled his now-aching shoulder and furrowed his browbone.

“well, this is …”

“trippy?” the other him suggested, raising half his browbone and shoving his hands in his pockets, though he looked anything but casual.

“not the word i’d have picked,” Sans muttered.

The other Sans shrugged. “works well enough. besides, _you_ did pick it.”

Sans’s eyelights narrowed. He looked the other skeleton up and down.

“you’re not me.”

“depends on how you look at it,” the other him replied, with a tone that suggested he could carry on an argument about this for two hours without breaking a sweat.

Sans stared for a second longer, then huffed and shook his head.

“i don’t have time to discuss philosophy.” He turned toward the gap’s exit, back toward the main part of the Core, where Papyrus and Alphys must already be far ahead. Far closer to the danger. “look, i … whoever or whatever you are, i’ll deal with this later, okay? i’m kind of busy there. there’s something going on out there and my friend and my broth—”

“H e ’ s _n o t_ y o u r b r o t h e r .”

It was so biting, so cold, that it made a shiver run up Sans’s spine. He turned to face the other him, and found his eyesockets completely dark, his smile tight and hard, his form imposing even though they must be exactly the same height.

Sans’s shoulders fell as the pieces clicked into place. The pieces that probably should have hit him right from the beginning. He let out a long breath.

“oh.”

Another browbone raise. “you kinda suck at reactions, don’t you?”

“what the hell am i supposed to say?” Sans spat, looking again toward the exit, then back to the other him.

“oh, i don’t know,” the other him drawled. “‘sorry for kidnapping your brother’ would be a good start.”

Something burned in Sans’s chest, stinging yet weighing him down all at once.

“i didn’t kidnap him.”

The other Sans made a sound vaguely like a snort, but without the humor. “you don’t seem too keen to give him back, though.”

Sans started to respond, but the words died in his throat. He looked at the other him a little more closely. He could see the dark circles around his sockets, the tightness of his grin. He wondered how many times his own face had worn that expression. He wondered if he was wearing it now.

“this wasn’t my idea,” he muttered.

“but you’re letting it happen,” the other him shot back. Sans stiffened. The other him narrowed his eyes. “i know your face. that’s _my_ face. you were never planning to even _try_ to get him back to his own universe.”

And this time, Sans didn’t try to respond. There was nothing he could say. The other Sans looked over him with unconcealed disgust.

“you’re even more pathetic than i thought you’d be,” he went on, and that burning feeling was back, sharper yet heavier than ever. “just because you weren’t strong enough to protect your own brother, you think you can go around stealing—”

Sans’s hand was up before he could think, bones shooting out of thin air, toward his other self. For a second, just a second, he swore they were going to hit. Then the other Sans ducked out of the way, the bones skimming the air just above his skull.

And Sans was left standing there, panting from the sudden effort, eyes wide as the other him looked at him with an expression that screamed “unimpressed.”

“like i said,” he muttered. “pathetic.”

Sans grit his teeth and scowled, but said nothing. He gave himself a moment to catch his breath, and found his eyes flicking over his shoulder, toward where he had last seen Papyrus and Alphys. When he looked back, the other him was still staring off into the distance, with something like longing burning in his sockets. Sans’s browbone lowered.

“if you’re so worried about me _protecting_ him, why don’t you let me go protect him now?”

The other Sans’s eyes snapped back to him, and the longing was gone just as fast as it had appeared. His smile curled into something closer to a grimace. “because if i let you go, you’re just gonna run and hide and take him with you. you’ll keep trying to pretend _you’re_ his brother. but you don’t know _anything_ about him.”

Sans could barely hold back a flinch, but he composed himself again, fighting back the urge to summon a bone and whack his other self over the head with it.

“if i’m so _pathetic_ for not being able to protect him, then what are you if you couldn’t hold onto him?” he hissed, though he took no satisfaction in seeing the other Sans tense under his gaze. “if he knows so little about you that he could just be plopped into some house he’d never seen with some guy he’d never met and actually buy it all this time?”

Except he _didn’t_ buy it. Not completely. He knew something was wrong, he knew Sans was different from _his_ Sans, even if Sans had deterred him, even if he hadn’t quite reached the right conclusion.

If Sans couldn’t stop him next time … if he managed to figure it out …

Papyrus might not know math or science, but he knew people. When he knew someone well, when he _loved_ them, he knew them better than Sans could imagine knowing anyone. Some things went right over his head, but other things he understood more deeply than anyone Sans had ever met.

Sans’s Papyrus would have known right away if Sans had been replaced. He would noticed the change in his demeanor from the beginning, maybe he wouldn’t guess that it was some alternate version of him, but he would know something was _wrong,_ and he wouldn’t stop until he had figured out what. If Sans had managed to fool this Papyrus, this whole time, if it took traveling across universes to make it clear that this wasn’t the brother he knew …

“you don’t tell him anything, do you?” Sans asked, before he had time to think. The other Sans just looked at him. Sans’s browbone lowered, and his hands curled into loose fists at his sides. “he doesn’t _know_ anything. your dad died, you _remember_ stuff about it, but you didn’t even _tell_ him?”

The other Sans jerked his head away, his smile gritted and tight.

“he wasn’t there when it happened,” he murmured, barely louder than a breath. His hands were shaking. “he shouldn’t have to deal with that.”

“you think you’re doing him a favor by keeping all this from him?” Sans asked, and he couldn’t tell whether his own voice held more sadness or anger.

The other Sans snapped his attention back to him. “like you’ve never done the same thing.”

“he _hates_ it,” Sans shot back, even as he felt the weight of guilt tugging at his own soul. “people call him an idiot—”

“he’s _not_ an idiot!”

“but you _treat_ him like one!” Sans cut him off.

Silence. Silence, filled by the blazing alarm Sans had entirely forgotten until now, the rushing of steam, the whirring of machines, the bubbling of lava. It was all so loud. But now it felt painfully quiet.

His breath came in huffs, his hands shaking where they had curled into fists, his sockets burning even though he knew he had no more tears left to shed.

“he notices stuff, you know! all those things you think you can just lie to him about, he _notices_! he knows you’re not being honest, he knows you’re treating him like he’s a little kid, like he can’t _take_ any of this! he’s _so strong_ and you hold him back and all you’re doing is hurting him because all he wants to do is help you and you won’t let him!”

And it hurt, goddamnit it hurt, he was a hypocrite and he swore he was looking into his own eyes rather than some him from another universe, swore he was seeing his own guilt, his own shame, his own pain as he realized exactly how badly he had fucked up. But as his own voice trailed off, his other self held himself taller, though his shoulders still hunched toward his skull.

“like you’re anyone to talk,” he muttered, barely loud enough to hear over the blazing of the alarm. “you kept stuff from him, too.”

Sans stiffened further. “how do you know?”

“because i know me.”

“i’m not you,” Sans snapped.

“you want to protect him. just like i do,” the other Sans retorted, and this time, there was no anger, no accusation in his voice. It almost sounded understanding. For a second. Just a second. Then his eyelights narrowed once more. “but you won’t keep him safe. you _didn’t_ keep him safe. you’re going to get him killed, just like you got your _own_ brother killed.”

The silence was going to drown him.

Sans shifted, and he swore he felt every tiny piece of his brother’s dust shift against his shirt underneath the jacket. But he didn’t look away. He stared at his other self, stared into his eyes knowing he was right, knowing every word was right and he was guilty, he had caused all of this, he should just give up and give Papyrus back to his real brother but he … he …

“the machine’s broken, you know,” he went on, very softly.

Another snort.

“wow, i didn’t notice. i thought the whole ‘crushed metal’ look was just an upgrade.”

There was no humor in his sarcasm, and he didn’t look the least bit surprised when Sans didn’t so much as smirk in response. Not that there was anything to smile about right now. His other self glanced to the side, in the direction where the machine might have been, very far away.

“i’ve been using it ever since your … dad showed up,” he went on at last. “it doesn’t just work for you, you know. it exists _everywhere._ that’s why it works, that’s why it lets you travel to the exact same point in all these different universes. it _exists_ everywhere. which means as long as it’s working, anyone can use it.”

His eyes returned to Sans, though he didn’t seem to be looking at him. Then he stared at the ground, his browbone furrowed, his smile tight.

“i didn’t know what it did when it first showed up. the room was there, sometimes, sometimes it was there, sometimes it wasn’t, but there was never anything _in_ it, and it was just … there. at least up until a couple days ago when i checked it last.”

His head tipped a bit lower, but raised again a second later. His sockets had gone dark. His permanent smile was trembling.

“then my brother disappeared.”

Sans swallowed. It was easy to forget, now, that it hadn’t been him that had yanked Papyrus out of his universe and brought him to his own. Because he wasn’t sure now whether he wouldn’t have done it himself if he had known it were possible. If his dad hadn’t done it first.

“so you started following us?” he asked, and though he tried to make his voice sound accusing, he couldn’t quite manage it.

“how could i follow you if i didn’t know where you were in the first place?” the other Sans asked, incredulous. “it’s not like that machine comes with a map.”

“it keeps tracks of coordinates. where you’ve been,” Sans retorted. He paused, a crease appearing in his own browbone. “is that why we ended up here after you did?”

The other Sans shrugged, as if it didn’t particularly mattered to him. “probably.”

“you didn’t know?” Sans asked. “you just hopped around universes, hoping you’d find us?”

And again, there was that tight smile, those dark eyes that would have felt strange on Sans’s face, but seemed far too at home on this one’s.

“you took my brother. i would have checked every damn universe _twice_ to get him back. ”

Sans had no trouble believing it.

If there had been a chance of his own brother being alive, somewhere, _anywhere_ …

“well, neither of us are getting back anytime soon now,” he muttered.

“i don’t care about that,” came the reply, again, without so much as a second’s hesitation. “i don’t care about getting back to my universe. i just want my brother.”

And it was true. Sans could stare at this other Sans as long as he wanted, and he could see, so easily, that Papyrus was the only thing that mattered to him in this or any world.

Those dark sockets darkened further, the smile tightened, and for a split second, Sans was actually afraid of himself.

“you can’t keep him. he’s not your brother. you got your brother _killed_ ,” the other Sans bit out. “and for someone who likes to go on about how much i keep from him, you seem pretty happy to keep lying to him now.”

There was nothing to say.

Sans looked at the other him, looked into the pained, longing, _determined_ sockets he probably would have seen in the mirror if he had bothered to look. This Sans wouldn’t give up. No more than _he_ would have given up if someone had taken his brother and he had thought there was a _chance_ of getting him back.

It had been him that told Gaster what he had done was wrong. That he couldn’t just go around stealing people from other universes.

That this Papyrus deserved better. Deserved a choice.

That everyone who loved him deserved to have him back.

But if he gave up this Papyrus …

_If he lost this one too he would never get him back he would be alone his dad was gone his best friend was gone everyone was gone he didn’t know if he was ever going home but at least he had his brother—_

“you think you’ve done so much better than me,” the other Sans drawled, mocking, his voice dripping with venom, and somehow he sounded infinitely older than Sans even though they must have been the same age. “but you’ve never had to take care of him.”

Sans stiffened, gritting his teeth. “we’ve always taken care of each other—”

“you had a _dad_ ,” the other Sans cut him off. “someone who stayed with you, someone who thought you were worth the effort not to get into _stupid_ experiments that would get him killed and leave you all by yourself.”

Sans paused, just long enough to lower his browbone and shoot a pointed glance to his right, in the direction he was sure Alphys and Papyrus still were.

“and what you think my _dad_ ’s doing now?”

A flinch. It was just a flinch, a flinch that didn’t do a goddamn thing to solve this mess, but it felt like a success. Like Sans had suddenly won one battle in this “whose life sucks more” contest with a version of himself whose brother he had stolen.

Then the flinch was gone, and the other him was glaring, eyelights sharp and hands curled into trembling fists.

He looked more tired than angry.

“you don’t know what it’s like. you _can’t_ know what it’s like, ” he bit out, and he really _did_ sound old there, so old, as old as his—their da—Gaster. “but you’d do the same thing i did. you’d lie to him if it meant protecting him. if it meant keeping him happy, if it meant keeping him _safe._ ”

A dozen different protests shot up Sans’s throat, and every one got caught behind his teeth. He said nothing. The other Sans pinned him in place with only a look.

“you’d do anything for him. just like i would,” he went on, even more confident than ever. No smugness. Just certainty. “it doesn’t even matter to you that he’s the wrong one. you’d take any one you can get. because you _need_ him. because he’s all you’ve got left. because he’s the only thing that matters in the world, the only person you can count on, the only one who will _ever_ love you so much.”

For a second, Sans stared into those wide sockets and saw himself. Not another version of himself, but _him,_ Papyrus’s brother, who had grown up at his side, grown up loving him more than anyone, who had sobbed over his dust until he passed out from sheer exhaustion.

Then those sockets went dark, and the smile below them twisted into something that threatened to rip him in two.

“but i’m not going to let you take him away from me.”

There were no words in Sans’s head, and even if there were, he didn’t think he could get his voice to work. Even when the other’s eyelights appeared again, they were sharp, faded, distant, and Sans found himself wondering whether, even if this Sans had never been through S.E., even if their HP was equally low, he could be killed by another version of himself.

Then the ground jolted under his feet, so hard he barely kept himself standing, stumbling forward and catching himself just as the other Sans bumped the back of his head into the nearest machine.

They looked at each other. They turned toward the exit of their little hideaway, toward Alphys, toward _Papyrus._

And finally, they heard the blaring alarm that had never stopped, even if neither of them had noticed it.

Sans moved without thinking, starting forward before he felt something grip his chest and yank him back. Only as the feeling dissipated did he recognize the heaviness of residual blue magic in his soul. The other Sans didn’t even look angry. Just irritated. Just … tired.

“he’s in danger,” Sans breathed even though he couldn’t breathe, Papyrus needed him, he had to get to Papyrus, Alphys would try to take care of him but she didn’t know him, she wasn’t _his_ Alphys, she hadn’t spent hours looking after them when they were kids she wouldn’t know what to do and that was his brother out there even if it wasn’t his brother and he had to—“whatever’s going on out there … he’s in trouble, and the longer you keep me here, the longer it’ll take for me to help him.”

He waited. The other Sans stared at him, and he stared back. Sans took a step to the side, toward the exit. The other Sans didn’t respond.

Then Sans took one more step, turning his head to face where his feet were already pointing.

“i’m not leaving.”

Sans winced, tilting his head just enough over his shoulder so he could make out his other self’s face. The other Sans watched him with eyes that really should have been more readable, given that he saw them in the mirror every day.

“i don’t care if you fix the machine,” he went on, his voice cold, hard, and far older than he really was. “i will follow you. wherever you go. i found you once, i can find you again. i’ll get him back. i’ll find him and i’ll do exactly what you seem to think you’re so good at: i’ll tell him the truth.”

Something like a shiver ran up Sans’s spine. Despite the heat sizzling nearby, it was the closest he had felt in his entire life to being cold.

“he’s not yours,” the other Sans finished, absolute, like a judge naming his sentence. “you can’t keep him.”

And as badly as Sans wanted to protest, he found he had nothing to say.

“Sans!”

“SANS!”

Sans jolted, but the other Sans didn’t even look surprised. Sans looked over his shoulder, toward the voices, not very far now, they were coming to find him, they had noticed he was gone, soon they would be here and they would see both of them and he couldn’t lie anymore then, Papyrus would know, he wasn’t stupid, he could look at two versions of his brother and know which one was his.

“he’s not calling for you,” the other Sans said, like driving in a nail.

Sans sucked in a breath through clenched teeth, looking behind him again as the voices echoed one more time.

“please.” He looked at himself, looked at this other Sans who had lived a completely different life, who had been through completely differently struggles, but loved their brother just as much as he did. “just … just give me time to fix this. just … let me help him. let me keep him safe. please.”

No response. Not even a blink. Sans curled his hands into fists at his sides, then forced them to relax.

“you can’t fix this. i _can._ i can get him out of here, make sure he’s alright, then you can …”

He didn’t finish. He wasn’t sure he even _could_ finish.

Saying it would make it real.

“go,” the other Sans replied at last, snapping him out of his trance. “i won’t be far away.”

Sans didn’t let himself wait another second. He turned around and ran back out of the narrow space as fast as he could.

If there was one thing he could say about the layout of the Core that hadn’t changed between the two universes, it was that neither made any sense. He knew what direction Papyrus and Alphys had gone in, but no path lasted long around here, there were too many turns, too many ways they could have gone. Papyrus’s voice had sounded close enough, but sounds echoed around here, and Papyrus was loud, louder than he had been before, he could be anywhere, Sans could be running even further away from him for all he knew, how the hell was he supposed to find him if he couldn’t—

He turned a corner and stopped.

There.

Maybe twenty feet in front of him, facing him, one foot off the ground as if he had been ready to run forward, as if he had been searching for him, too, Alphys at his side with relief shining in her eyes, and nothing else mattered not the alarm not Gaster not the other Sans because _Papyrus was here and he was still okay._

“SANS!”

Sans started to say something, even if he didn’t know what it was, even if he didn’t know what excuse he could give, even if he didn’t know what he was supposed to say to this person who he was going to lose, who he _had_ to lose, because he wasn’t his to keep he had a brother and it wasn’t Sans and he was going to lose him again he—

He didn’t get the chance.

Papyrus crossed the distance between them in mere seconds and scooped him up into a hug, squeezing him tight.

“WHERE DID YOU GO?” he asked, somewhere between a shout and a whine. “WE DIDN’T SEE YOU LEAVE BUT YOU WEREN’T THERE AND WE THOUGHT YOU MIGHT HAVE FALLEN IN AND WE WERE REALLY REALLY WORRIED DON’T YOU DO THAT AGAIN BROTHER OR I WILL BE VERY UPSET!”

His hugs felt the same.

Sans hadn’t had the time to consider it yesterday, when he was pulled into a tight embrace against the brother who wasn’t really his brother. Hadn’t had the time to compare all the little things that he should have noticed because this was his _twin brother_ and they had been together since before they were born, he should _know_ things like that. He had thought that once he knew, he would be able to notice them. But he didn’t. Papyrus hugged him, and it felt for all the world like all the hugs he had received over the past nineteen years.

He barely had the clarity of mind to reach his arms around and hug him back, it was wrong, it was all wrong, this wasn’t the right brother, but he wanted it he wanted it more than _anything_ and he would never have it again so why couldn’t he just enjoy it? He closed his eyes, just for a second, before he forced them open again, gritting his teeth as he tightened his grip around the person whose dust he could still feel lingering on his shirt.

“s’okay, bro. it’s fine,” he murmured, his voice distant and weak and he never wanted Papyrus to let go even with the alarm blazing around them he couldn’t stay here no matter how bad he wanted to. And sure enough, a few seconds later, Papyrus gave him one final, tight squeeze, letting him slip back down to the ground. Sans jerked his gaze to Alphys, straightening himself before he had the chance to miss his brother’s warm touch. “alph? where are we headed?”

Alphys stiffened, like she had been caught doing something she wasn’t supposed to, and only then did Sans notice that she had been staring at them with an odd, almost affectionate look on her face.

Only then did Sans remember that this Alphys had never looked at him like that before.

She cleared her throat and turned around, pointing one shaky claw in the other direction.

“I t-think this is the right way. I ch-checked the readings on m-most of the m-machines on the w-way and n-nothing was wrong, so …”

Sans nodded, even though he knew she wouldn’t see, and started forward. Alphys seemed to take this as her cue and began walking as well, slower than she had before, as if she were fighting with her own sense of duty and the fact that she really, really didn’t want to go any further than she already had.

“do you have any idea what’s wrong?” Sans asked.

Alphys bit back something like a whine and shook her head.

“I … I-I’ve never seen anything like t-this before … I d-don’t …” She pursed her lips, squeezing her eyes shut and taking a deep breath before nodding to herself. “W-we’ll figure s-something out. I- _I’ll_ figure s-s-something out. Dr. G-Gaster t-trusted me to … I-I’ll f-fix it.”

She was scared. She was terrified. But she was also far more determined than Sans had ever seen his own Alphys, and he wasn’t sure whether or not to view that as a comfort.

She looked to Sans, then over her shoulder at Papyrus, biting her lip.

“You guys s-should r-really go back, t-though.”

Sans didn’t need to turn to imagine Papyrus standing up a little straighter, as if in stubborn defiance, and he allowed himself a smile that felt a little closer to being real.

“sorry, alph,” he replied. “not a chance.”

Alphys frowned, but she looked ahead again without another word.

As they walked, Sans found himself glancing behind him every minute or so, not just checking on Papyrus, but making sure that the other Sans wasn’t following them. Of course, even though Sans never saw him, he was almost sure he was there. But as long as he wasn’t close, as long as he didn’t have the chance to snatch Papyrus up when he wasn’t looking, as long as he couldn’t take him not yet not yet he wasn’t ready _not yet_ —

Sans fidgeted more with every corner they turned, the deeper into the Core they went. Something was wrong. He didn’t know what, it didn’t feel like the wrongness of being watched, he didn’t know _what_ it felt like, it just felt … wrong. Wrong like the Papyrus that wasn’t _his_ Papyrus, the Alphys that wasn’t Alphys, the Gaster that wasn’t Gaster, Dr. Japer and Dr. Lemming and Dr. Frewth all _dead._ Wrong like the silent worlds, covered in dust.

Wrong like the world of nothing, empty, dark.

They were close.

He didn’t know how he knew it, but once the thought came to his head, he had no doubt.

Alphys wrung her hands and glanced at one of the machines they passed, though Sans didn’t recognize it. Then she turned ahead again, fighting against the obvious urge to hunch into herself, biting her lip so hard it was a wonder she didn’t split it down the middle.

“J-just a l-little f-further. W-we—”

Alphys’s words cut off in her throat as she jerked forward, like something had hit her, but nothing had hit her, he would have heard it, he would have seen it, but now her face was scrunched up like she was in pain and even over the alarm he could make out the whimpers that slipped past her lips.

“alph? alphys?” Sans called, reaching out to her with hesitant hands, he would have hugged Alphys, but this _wasn’t_ Alphys, he didn’t know how she’d take it, and suddenly he didn’t have time to think about it when another cry of pain, just to his right, made him jerk his head to face it. “pap!”

If Papyrus could hear him, he didn’t respond. He clutched his head and hunched over like his skull was aching, like his skull was about to _explode,_ his teeth clenched and his sockets squeezed shut. For a second it looked like he had changed position, then a second later he was hunched over again, then again and again, back and forth, faster than a person should be able to move.

And his clothes. His clothes were changing, too, the color, the shape, and Alphys was doing the same thing, it was like he was looking at a hundred different people flashing in and out of existence every second.

They were … flickering.

Like a movie. Like one of those really old movies Alphys had found when she was looking for new anime and she called him over to her house like she sometimes did when she wanted someone else to watch with and she knew he didn’t like anime but he always came, but this time it wasn’t anime, it was something with real humans, no sound, just flickering, jolting images flashing in and out on the screen.

But this wasn’t a movie.

His friends were flickering.

And he wasn’t.

He looked down at himself to be sure, but there was nothing out of the ordinary. Just him in that stupid blue hoodie he loved more than he had any right to and his dirty T-shirt and shorts and shoes. Something was hurting his friend, hurting his _brother,_ and it wasn’t hurting him.

Wasn’t hurting him because he …

He …

He didn’t realize he had moved until his hands were on both of them, pushing them back in the direction they had come, he could feel them changing under his hands, they weren’t walking right, it was a miracle they were moving at all, but they _were_ moving and that was all that mattered.

“S-SANS?” Papyrus managed, and it was like his voice was flickering too, it was _his_ voice, it never stopped being his voice, but it changed, shifted, cut in and out. “W-WHAT-T’S—”

“it’s gonna be fine, bro, it’s fine, we’re gonna get out of here,” Sans murmured, as much to himself as to Papyrus, pushing him along faster still.

They took a few more steps, further away from whatever was causing this, and bit by bit, the flickering slowed, until it finally stopped entirely, but Sans kept walking, get away, have to get them both away.

Only a few seconds had passed since she stopped flickering, since her head had lifted from her hands, but Alphys was already struggling, trying to look over her shoulder, to turn around, even though her feet never stopped moving.

“B-b-but I n-need to—“

“alphys, you can’t help anyone if you can’t go in there safely yourself!” he cut her off. She looked at him, eyes wide, pleading, and Sans grit his teeth and shook his head. “we’ll … we’ll figure something out, i’ll help you, but right now, we gotta go.”

“I-I …”

But she didn’t stop. She kept going when he nudged her forward, and that was all that mattered. Get them out. Get them out, then he could figure out what the hell he was going to do about the rest of this.

He had already known, of course. He had already known that something going wrong here had to be related to Gaster, and when it was something like _this_ … well. Sans might have believed in coincidences, but not if they were ridiculous.

Not anymore, at least.

He found his gaze drifting back over his shoulder as he ushered Alphys and Papyrus out, back toward the exit, though he jerked his head forward before Alphys had the chance to notice and think it was her cue to try to go back again. She couldn’t go back. She wouldn’t be able to get close without hurting herself, and this wasn’t her problem, this wasn’t anyone else’s problem but his.

No one else was going to stop him. Because no one else _could_ stop him.

Whatever Gaster had done was affecting every monster, except those who had absorbed enough S.E. to resist it.

This Papyrus, as far as he knew, had never had any more S.E. than what he had had at his creation.

That left Sans.

Just as it should.

Alphys was still muttering to herself about responsibilities, she had to do something, it was her _job_ to do something, but she didn’t resist Sans’s attempts to move her forward, and Papyrus was still clutching his head and stumbling ahead on more reflex than anything else.

He was going to get them out of here. He was going to make sure they were safe. Make sure that no one else would be caught in the crossfire, no matter what happened. No matter what Gaster had done, and no matter what it took to stop him.

Sans had gotten them into this whole mess. And one way or another, he would be the one to get them out of it.

**Notes for the Chapter:**

> Just to make something clear: I, as the author, am well aware that Papyrus does not belong to anyone. He is his own person, makes his own choices, and should be fully informed about the situation he is in. Sans is a hypocrite and is making poor decisions. I am also aware of this. At the moment, he's still in a messy position (both he and Papyrus are still the victims of Gaster's mistakes here) and isn't thinking straight, but later on, he will not have that excuse and will need to face the fact that he isn't treating his brother with the respect he deserves. This story is very, very long and there is a LOT left to cover.


	50. 0

If Papyrus had been home, he probably would have broken down the door by now.

Well, maybe not. Papyrus had more respect for their house than Sans or their dad, and he probably would have found a less-violent way to get into Sans’s room. But he would have gotten in, one way or another, and he would probably be standing in front of him, giving him a very firm, very loud pep talk of exactly why sitting in his room and brooding wasn’t going to solve any of his problems, how he needed to have confidence in himself, how everyone else believed in his abilities and all he needed to do was believe it, too.

Sans couldn’t decide whether he wished Papyrus would come home early.

But as it was, Papyrus was still out—probably at the grocery store, picking up ingredients for the “celebration cake” he hadn’t been able to keep a secret—and Sans sat in his room alone, on the edge of his bed, staring at the floor and resisting the urge to bang his skull against the closest wall.

It had seemed so easy, four years ago, when he had started his doctoral degree program. Hell, it had seemed so easy just a few _weeks_ ago, when he had first begun preparing for his graduation. He had known he would be graduating this semester. He had planned everything out from the beginning, he had taken all the courses he needed—plus a few extras, just out of curiosity—and he had completed all the requirements to earn his degree.

But now he was really going to _do_ it.

He had been in college for seven years now. And … he was about to be done.

Technically speaking, he _was_ done. His exams were completed. His thesis had been written and edited and defended. He had been approved as a doctoral recipient.

Funny, how something that had once seemed so exciting had flipped to “terrifying.”

This was what he had wanted, wasn’t it? He _wanted_ to be a scientist. He _wanted_ to work in the labs. He had already been accepted there, for god’s sake, he had a job lined up, his _dream_ job, what did he have to complain about? He had done it. After all these years, after all this work, he had _done_ it. And … he deserved it, didn’t he?

That was what everyone had said. He had exceeded all expectations, finished years before most of his classmates would. He was about to become the youngest doctoral graduate in the history of the underground’s university. Everyone was proud of him. Everyone believed him.

He just didn’t know if he deserved it.

Everyone thought he was going to do amazing things. Everyone thought he was going to be amazing right from the start, he was going to churn out astounding, mind-blowing work, and he had thought the same thing for years, but now … he was there. Those expectations were _real._ What if he couldn’t meet them? What if he wasn’t as brilliant as everyone seemed to think he was? What if what everyone was seeing … wasn’t who he really turned out to be? He had interned, sure, but it wasn’t like he had done any _real_ work, and even if he had, having a real job … that would be different. People would be counting on him. Counting on him to help them, counting on him to do something important.

He was the genius kid of the Royal Scientist. That was what he was _supposed_ to do.

What would happen if he failed?

What would they think of him? What would his professors think of him, his fellow classmates—who had taken years to even begin to respect him once they found out his age? What would his _dad_ think? He had been so proud of him when he made that device at the science fair all those years ago, when he graduated high school, when he started college, got his Bachelor’s, started his PhD. Even when Sans insisted that his dad appreciate his brother for his own qualities, even if they weren’t Sans’s … that was still so much of what he heard his dad talk about. When it came to him, it was almost _all_ he heard him talk about.

If he failed at this … if he couldn’t be everything everyone thought he could be … what would his dad think of him then?

He didn’t know how long he had been sitting there when he heard the footsteps outside his room. He did his best to loosen the grip of his arms around his torso, but still found himself curling up more. He straightened a little when a knock sounded at the door, and had to wait only a second before a gentle voice followed.

“Knock knock.”

Sans wasn’t sure whether he wanted to laugh or groan, so he didn’t do either, even though he could hear his dad smirking through the door.

“Who’s there?”

“Boo.”

Sans rolled his eyes, but still managed not to groan. “… boo who?”

A faint chuckle, echoing through the wood. “It’s only a joke, you don’t have to cry about it.”

And Sans was smiling—more than just the smile stuck to his face—and he hated it, why the hell did he have to find jokes like this funny when he was in a bad mood? He shook his head and let the faintest of laughs slip out of his throat before he forced the it back. The knob turned and the door creaked open, revealing his dad’s smiling face. Sans looked away, but he couldn’t quite hide the smile that still curled up the corners of his mouth.

“You’re lucky Papyrus isn’t home,” he murmured, just loud enough to be heard from across the room. “Apparently he met a monster a few days ago who told even worse jokes than you and he’s still touchy about it.”

His dad chuckled and smiled wider, though there was an odd, quiet sadness behind it now.

“May I come in?”

Sans looked back to him in full, hesitated, then gave a short nod. “Yeah.”

The door opened the rest of the way, and his dad stepped in, pushing it shut behind him. He stood there for a moment, just looking at Sans, his expression soft, before he crossed the room to sit on the bed next to him. Sans started to say something, something to brush away his dad’s worries, but nothing came to mind. There was no point lying now, as much as he might have wanted to. He had been obvious enough the past few days, he was sure, and he had already given up hope on putting on a happy front.

“Nervous?” his dad asked after a minute of silence, tilting his head and giving him a sympathetic grin.

Sans started to say yes, but stopped himself and huffed a sigh. His dad didn’t push him. He just sat there, waiting, as patient as he had ever been.

It had been years since he had finished the Core, years since he had started taking evenings, weekends, and even some full days off to spend time with them. He should have been used to it by now. He should have been used to his dad not constantly being in a rush. But he wasn’t. Now, he wasn’t sure if he would ever be.

Now … it didn’t really matter, did it?

Because he would be _working_ with his dad. They would be in the same building, if not the same lab, all day. He would finally get to spend time with him, as much time as he wanted, just like he had when he was a kid. He had almost forgotten how much he had wanted that. He had given up on it, so many years ago. Just … accepted that it wasn’t going to happen. His dad loved them, but he was just too busy.

He had too many important, _essential_ things to do.

_No experiment is more important to me than the two of you._

He had said that. Sans could still hear what his voice had sounded like, four years ago, when he had skipped out on a work assignment because Papyrus had a bad day at school. But it wasn’t true, even if he believed it. They were just two kids. What his dad did … it was essential for _everyone._ He had built the Core. He had prevented an energy crisis. He had worked for the good of monsterkind for centuries before Sans or Papyrus was born. He had done more than Sans could even imagine.

And Sans would be working alongside him.

If he couldn’t match up to that … how the hell could he _ever_ match up to someone like …?

“Sans?”

Sans jerked his head up—when had it fallen?—and faced his dad again. He stared into two wide, concerned eyesockets, frozen for a moment before he let his head drop again. He felt his dad touch his shoulder. He closed his eyes, letting out a long, heavy sigh.

“Am I good enough?”

Silence.

Sans waited for at least ten seconds before he looked back up, slowly, carefully. If his dad’s eyes had been wide before, it was nothing compared to how they looked now, so wide that he almost couldn’t tell the difference between his dad’s bad eye and good eye. A small crease formed in the center of his browbone.

“I do believe that may be the strangest question I’ve ever heard. And I’ve heard quite a few,” his dad replied, with a tone to match his expression. He shifted a little closer, not quite touching Sans’s side. “What do you mean?”

Sans ducked his head a little lower, clutching his arms close to his body and staring at the floor.

“I mean … am I … can I do this? Can I actually do this?” His smile tightened, and he shook his head. “I … I’ve done it so far, but … sometimes I still feel like this little kid walking around with the big kids, and they all know exactly what they’re doing and I have no _idea_ and I pretend but nothing helps and it doesn’t matter what I do, I’m still just a little kid and tomorrow everyone will _see_ that. They’ll realize I … I have no idea what I’m doing.”

He swallowed the lump growing in his throat and forced himself to look up before he could think better of it. His dad was still looking at him, wearing one of those expressions Sans had never been able to read. One day, he swore, he was going to be better at that. Life would be so much easier if he could just tell what his dad was thinking without having to wait for him to say it.

It took nearly a minute before his dad finally spoke.

“Have I ever told you about my favorite accidental experiment?”

Sans stared. Then he dropped his head and groaned.

“ _Dad._ ”

“Well, have I?” his dad asked again, and Sans didn’t have to turn back around to hear him smiling.

Sans huffed a sigh, and shook his head.

“I lost count at two hundred times, Dad. I think I know this story better than you do at this point.”

“Ah, well, then there’s no harm in hearing one more time. Who knows? Maybe you’ll learn something new,” his dad replied. He was definitely smiling now. Full-out grinning, by the sound of it. “Once upon a time—”

“Dad!”

“ _Once upon a time,_ approximately nineteen years ago, there was a scientist who thought it would be a good idea to leave two shards of his own bone in a mason jar filled with a certain liquid experiment he had lying around. Much to his surprise—”

“—he came back on Monday and found that the two shards of bone had grown into two itty bitty skeletons, who grew into his kids, Sans and Papyrus, and they all lived happily ever after, until Sans got his first job and turned out to be no good at any of the stuff he spent seven years studying in college and failed everyone who ever believed in him. The end.”

He faced his dad as the last words left his mouth. Both of them looked at each other for a good twenty seconds. Then his dad raised half his browbone, a faint smirk on his mouth.

“You never did like letting me finish stories.”

Sans rolled his eyes, but looked away again. “Fine, whatever. Go ahead.”

His dad chuckled.

“ _Much to his surprise …_ he came back Monday and found that two shards of bone had grown into two itty bitty skeletons, who grew into his kids, Sans and Papyrus.”

Sans tilted his head enough to give his dad a look. But the look faded when he found his dad’s eyes softer than before, his smile gentle, affectionate. Nostalgic.

“And the scientist was terrified,” he went on, more quietly, his eyes shifting down to the bed, faint creases on his bone where worry lines must once have been. “He had never planned to have children. He was very old, and he had never had a partner, and the rest of his family had been gone a very, very long time. He had absolutely no idea how to care for the two little boys he had inadvertently created. He loved them so much, but he didn’t know if he could take care of them. He even thought … perhaps they would be better off with someone else.”

He didn’t look up. Sans’s chest twisted, and he felt his permanent smile tilt down until it almost didn’t count as a smile anymore. But after only a few seconds, his dad lifted his eyes, his own mouth settling into an easy smile that soothed the ache in Sans’s chest, twisting it into confusion.

“But the moment he held him in his arms, he knew he couldn’t let them go. It was the first time he had seen another skeleton in centuries, and he had forgotten … he had forgotten what it was like, to not be the only one of his kind.”

Sans shifted a little on the bed. His dad’s smile widened, and he lifted a hand to rest it on his shoulder.

“But more than that, far more than that … he had never imagined how special they would be. How much he would grow to love them for who they were, not just because they were his. How intelligent and talented and compassionate and enthusiastic and _precious_ they would be.”

Sans looked down. He wrung his hands in his lap, and he swore he felt a faint warmth on his cheekbones.

“Did the scientist ever figure out what he was doing?” he asked, his voice as quiet as he had heard it in months.

His dad chuckled and squeezed his shoulder tighter.

“Not for a second,” he said. He touched the fingers of his other hand to Sans’s jawbone and tilted his head up to look at him. “And it still scares him, because he wonders sometimes if one day, he’ll finally fail them. If one day, he’ll finally make the wrong choice. If … he won’t be able to protect them, just like he couldn’t protect all the other people he loved.”

His dad’s face fell as the words left his mouth, and for a second, just a second, Sans could see all the pain hidden behind the lights in his eyes. Everything he had never told them. Everything he might keep to himself for the rest of his life.

Then the smile was back, and he met Sans’s eyes once more, his own filled with so much love it made Sans’s chest hurt.

“But he still tries. He’ll never stop trying. Because those two itty bitty skeletons are far too important for him to give up.”

Sans swallowed against the lump in his throat, and fought against the impulse to look away. His dad kept smiling this time, the brief rush of grief entirely gone. Sans sat up a little taller, a little less hesitant, a little more hopeful.

“Do you think I can do this?”

His dad smiled wider still.

“I’ve always thought that. I’ve always _known_ that,” he replied. “If you put your mind to it, you can do it.”

Sans was nineteen years old, but he felt like he was nine, standing in front of his science project at the fair, watching his dad’s eyes light up in pride at his creation. He had made it because it was fun, because he wanted to try something new, he wanted to help, but he had stuck with it, devoured all the information he could find, on the simple hope of seeing that look again.

“You’re going to help so many people. You’re going to do so much good. I have no doubt about that,” his dad went on, making Sans’s chest swell even more than it already was. He huffed a laugh, a glint of amusement in his eyes. “I wouldn’t be surprised if you take my position in a few years.”

Sans bit back a sputtering laugh, staring back with wide, baffled eyes.

“Dad, c’mon! _You’re_ the Royal Scientist, I’m just …”

He trailed off. His dad squeezed his shoulder one more time, his face softening.

“You’re not _just_ anything. You’re Sans. You’re my son. And you’re going to be amazing,” he went on. Sans looked down at his hand on his shoulder, only for his dad’s fingers to flick him between his sockets. He tried to scowl, but only ended up smiling. His dad smiled back, looking at him with so much warmth it almost hurt. “You already are.”

Sans’s smile stretched so wide its hurt, and he could feel his eyes gleaming so bright they could have lit up the room all on their own.

Before he could get out a word, they both turned at the sound of the door opening downstairs, a set of footsteps entering the house before the door shut once more.

“Sans! Dad! I’m back! But don’t come down yet, I have things to put away which are not for your eyes to see!”

Sans couldn’t hold back the snort that forced its way out of his nasal passage, and apparently, neither could his dad. They looked at each other and bit back their chuckles.

“I really couldn’t ask for a better brother,” Sans said, and even though he was still laughing, the words had never sounded more sincere.

His dad’s eyes softened further. “And I could never ask for two more wonderful boys.”

Sans’s cheeks warmed again, but this time, he didn’t look away. His dad’s hands rested on his shoulders, pulling him in for a brief hug before pushing himself to his feet.

“I’ll go help Papyrus put away the … things,” he went on, prompting another chuckle from Sans. “I’ll call you down in a minute.”

Sans just nodded, smiling with more ease than he had in weeks. His dad smiled back before turning around and walking out of the room. Sans’s shoulders sagged a little once he was gone, but this time, it was like letting go of a heavy weight, rather than gaining it. His soul thrummed, warm and relaxed, in his chest, and his worries had never seemed further away.

He could do this. He was _going_ to do this.

He would help everyone. He would find a way to do something important, something that would make everyone’s lives better. He would live up to the expectations that had been placed on him. He would _exceed_ them. He would be the best son—the best _brother—_ that his family could have asked for.

And he would make them happy. He would change the world, change _their_ world. Be everything they had ever hoped he would be and more.

No matter what it took.


	51. Chapter 42

“W-what? We’re not j-just …”

“SANS, YOU AREN’T STAYING HERE! THIS PLACE IS DANGEROUS AND THIS IS NO TIME TO BE TOO LAZY TO MOVE! IF WE’RE LEAVING, YOU’RE COMING, TOO!”

Sans had known that it wasn’t going to be easy to get the two of them to leave without him. Honestly, now that he really thought about it, the idea was downright stupid. Alphys barely knew him, but she was kind, compassionate, and Papyrus …

… Papyrus wasn’t going to leave Sans behind. It didn’t matter that it was a different Papyrus. He would sooner fling Sans over his shoulder and carry him out that way than let him stay here while the two of them left.

But that didn’t change the fact that these two needed to get out of here, and Sans needed to stay.

“look, there’s … there’s something i need to do here,” Sans tried, and almost smacked himself as soon as the words left his mouth.

“W-what?”

“WHAT DO YOU NEED TO DO HERE, SANS? YOU’VE NEVER BEEN HERE BEFORE, HAVE YOU? HOW COULD YOU KNOW ANYTHING ABOUT IT?”

Alphys was giving him that look again. That look he had been trying to avoid, the look that showed a few of the pieces clicking in her head, that look that meant she was creeping closer and closer to the truth. Sans swallowed and shook his head.

“i … nevermind,” he murmured. “it’s nothing. let’s go, okay?”

The look didn’t go away. He knew it wouldn’t, he was an idiot, he knew they weren’t going to leave without him, but he had to go back, he had to find a way back, he would just get them out of here, distract them, then go back himself. It would waste time, it would be more than difficult to shake them now that they were suspicious, but it was the only plan he had.

They both stared at him for a few seconds, and he knew they didn’t believe him, of course they didn’t believe him, they weren’t stupid, they _knew_ him, but they said nothing. They turned around and ran back toward the exit, and Sans forced himself to follow.

Just long enough to shake them. Just long enough to make sure they were safe.

They ran, turning corners without thinking, the clanking of the metal beneath their feet just loud enough for Sans to hear above the blazing alarm. Papyrus turned back to look at him every few seconds, as if to check that he hadn’t slipped away, and Sans didn’t even try to smile back at him, there was nothing to smile about, no energy to fake a smile, so he just kept running and they were close now, they would be out of here in just a minute, he could—

The Core jolted.

The ground shook underneath him, throwing him to the left, to the right, the floor jittering and threatening to topple him at any second. Alphys stumbled and fell to her knees in front of him, and Papyrus, already near the edge of the landing, teetered to the right.

Toward the pit of lava below.

Sans reached up a hand, ready to grab his soul, no, _no,_ he had already lost him, he couldn’t lose him again, not again, it didn’t matter if it wasn’t really him it was still Papyrus, have to keep him safe, have to protect him, the magic formed around his hand and he held it out just as Papyrus began to fall.

But before his feet could leave solid ground, something shot through the air and hit him, knocking him away from the edge and back onto the floor.

Two people crashed onto the landing, shaking it further even as it started to steady. Sans blinked away his shock and let the magic fade from his head, taking in the blue, scaly skin and long red ponytail of the woman pinning Papyrus to the ground.

For a few seconds, they all froze, Sans and Alphys gawking, Papyrus staring up at his rescuer, and the unnamed woman looking down at Papyrus with something between anger and fear.

Then her head snapped up, her teeth bared in a scowl.

“What the hell are you guys doing here?!” she spat, looking around at all of them with a strange mix of authority, anger, and utter terror. “This place is dangerous, we ordered everyone to _evacuate,_ not—”

“UNDYNE!”

The lady had only a couple of seconds to look down at Papyrus’s face before he threw his arms around her, tackling her in a full-body hug. She tensed, but didn’t fight it, and Papyrus squeezed her hard enough to break her bones.

“Undyne” blinked and stared at him, not hugging him back, but not pushing him away. “Uh … yeah, that’s my name. Have we met?”

“UNDYNE, YOU'RE REALLY HERE!” Papyrus said, as if he hadn’t heard her, or as if it didn’t matter. He rubbed his head against her shoulder and hugged her tighter still.

Undyne raised an eyebrow, and somehow managed to lift one of her hands enough to pat him on his skull.

“Uh … sure, buddy,” she muttered. There was more than a little confusion in her voice, but the longer she looked down at him, the softer her eyes grew, and her rough patting softened to something that could almost be considered petting. Her mouth twitched up at the corners, and she huffed a laughing sigh. “Sheesh, and here I thought I didn’t have any fans.”

Papyrus didn’t respond. A few seconds later, she pushed herself up off the ground, and though Papyrus resisted for a second, he let her stand up, climbing to his feet beside her. Sans snapped out of his own reverie and crossed the space between them faster than he had thought was possible, wrapping his arms around his brother in a gentle, yet firm, embrace.

He felt two hands rest on his back, rubbing up and down, and he let out a long, shuddering breath he didn’t realize he had been holding.

Safe. He was safe.

He was going to be okay.

Everything was going to be okay.

As long as Papyrus was here, as long as he was _safe,_ everything would be okay.

When he forced himself to pull back, Undyne had apparently lost interest in the strange skeleton that had tackle-hugged her, and turned her attention to the one person who, up until now, had apparently been trying to make herself invisible.

“Alphys?” Undyne asked, brow furrowing, good eye wide and blinking in an emotion Sans didn’t know her well enough to name.

But while Sans might not know _her_ face, he knew Alphys’s. Even if it was the wrong version of her, her expressions didn’t change that much. And he could easily pick out the rush of mixed anxiety and affection that matched the expression she had worn earlier that same day.

“Uh, h-hi U-Undyne …”

“You’re supposed to be safe at home!” Undyne snapped, but there was too much genuine concern behind it to call it angry.

Alphys fidgeted. “But y-you’re here t-too!”

“I’m making sure everyone’s out safe!” Undyne shot back. She looked to Papyrus, then Sans, then scanned their surroundings as she straightened up, claiming charge of the situation without a word. “And you’re the last three, so come on, we’re getting you out of here.”

For a second, Alphys just stared at her, wide-eyed, frozen. Then it was like a switch went off in her head, and she held herself a little taller, curling her hands into fists and setting her mouth into a tight, determined line.

“R-right. Right. Let’s go.”

Undyne flashed her a frighteningly wide grin, then nodded and started toward the exit at a pace Sans suspected was only about half of her top speed, but which still forced Alphys and Papyrus to sprint to catch up.

They were both far too focused on the woman leading them to notice that Sans had stayed exactly where he was.

He allowed himself one more look at Alphys, one more look at her friend, that Undyne, who had gained Papyrus’s attention and affection even though Sans had no idea who she was.

He looked at Papyrus, who had held him like his brother had held him, who stroked his head and encouraged him and looked at him with warm, loving eyes he had thought he would never see again.

Papyrus would be safe here.

No matter what happened, if Sans stopped Gaster …

Papyrus would be safe.

Sans turned around and ran back into the depths of the Core.

He didn’t think about where he was going. He didn’t need to. Maybe it was physical memory stored deep in his bones, maybe it was instinct, maybe it was something else entirely. Either way, he kept moving. As he got closer, something inside him felt … odd, odd but not _bad,_ not like Alphys and Papyrus, standing there clutching their heads. He was still moving, he was still solid and secure, he was _himself,_ but it was like something was tugging at his entire being and it knew it would never win but it kept trying anyway.

His eyes were locked ahead of him, and he wouldn’t have noticed it if it hadn’t been standing just out of his line of sight.

The flash of white, like a glob of paint, off to his right, contrasted against the gray and red and orange all around them.

Standing still, looking around, disoriented, lost.

Him. The other him.

But … the other him had been in a gray hoodie. He was _sure_ he had been in a gray hoodie.

So why was this one wearing a lab coat?

Sans jerked his head away and ran faster, even as the image of two other hims latched onto his head. Less than a minute later, he saw another in the corner of his eye, looking around him, and another after that, and another, they were all over the place, scattered, some in different outfits, some calling out to him, some calling out for Papyrus, one even tried to grab him as he passed, but Sans never stopped. Keep going. Have to keep going.

It was getting stronger. Every step he took, stronger and stronger, he was close, he just had to get there, get there and stop all of this, keep everyone safe, no matter what happened to him at least Papyrus would be safe.

He reached another corner and swung himself around it.

Then he stopped so fast he almost tripped over his own feet.

Because there was someone in front of him. Maybe ten feet away.

Standing in the center of the catwalk, bubbling lava far below him on his right, a wall of machines on his left, facing him with wide, blank sockets.

It was … his dad.

But it _wasn’t_ his dad.

It was … wrong. It was so, so wrong and it hurt to look at and he wanted to turn around and run and never come back but he _couldn’t make himself move._ He had forgotten how to move, how to breathe, how to speak. All he could do was stare at the thing in front of him, the thing shaped like his dad, the thing that _was_ his dad, but it … wasn’t.

It looked like him. It looked _so much_ like him yet at the same time Sans had never seen anyone look more different. It looked like a thousand people at once, a _million_ people at once, one second he would look at him and he would swear the person he was looking at was his dad but then a second later it wasn’t and god, what was going on, this didn’t make any sense, he didn’t know what was going on and—

That was his dad.

He knew it. He knew it to the very core of his being, but he didn’t want to believe it.

He was shaped the same, mostly. But he was … loose, like whatever was making him up had begun to fall apart but not enough to truly make him lose form. Like Sans had felt when he had too much S.E. at once, like he was melting, but Gaster didn’t _keep_ melting, he was melting and reforming so fast Sans could barely see it, like his body didn’t know how to stay together but it couldn’t fall apart either. There were cracks on his face but there _weren’t_ cracks on his face and his black coat was melding into a white lab coat and there were holes in his hands _why were there holes in his hands_ then there weren’t there anymore he was missing limbs but they were regrowing, too many, all at once, he couldn’t count, he couldn’t see, he couldn’t _think._

“what did—what—what did you _do_?! ” Sans sputtered, shifting from indignant to horrified to terrified to _furious_ so fast he could barely feel the change. But Gaster just stood there, staring ahead of him, his eyes wide and blank, his limbs hanging limp at side even as they flashed in and out of existence, could he even move with his body shifting so fast, Sans didn’t care, he had done this, _he had done this to himself._ “ gaster? _gaster?!_ ”

“Gaster.”

It was like listening to a computer try to figure out how to pronounce a word it had never seen, like listening to a thousand different computers try at once. Something flashed across Gaster’s face. Something like recognition.

“W.D. Wing Dings Doctor Gaster,” the voice went on, Gaster’s head tilting to the side. “I am Gaster. We are G̖̹̜̞͍̬̰a͎̮͈̜̯s̯̘̼̹t̜̝e͎̲͔͉͜r̨͎͈̱̟̩ͅ.”

Sans grit his teeth so hard he could feel them threatening to crack. “what do you mean, _we,_ what are you—“

“All of us,” Gaster went on, as if he hadn’t spoken. “All of us together, all together, all at once. Together we’re … together we’re strong enough.”

Sans was shaking, his whole body shaking so hard he could almost hear his bones rattling above the blazing alarm, nothing made sense, everything was _wrong,_ he wanted to get away but he couldn’t even blink.

“what the hell are you _talking_ about?”

Gaster looked at him, but he _wasn’t_ looking at him, it was like he was seeing all of him and none of him at once, his head straightening out before tilting the other way.

“Core exists everywhere. S.E. is … everywhere. All universes, all at once, it’s strong, it stays, makes the machine stay, makes me stay, too.”

Sans started to reply, to shout back, to demand the know what was going _on._

Then his eyes lowered, just a bit, enough to stare at Gaster’s chest.

And he saw it.

The S.E. core.

Sans could see it now, the red glow shining through his shirt, just as he made out the thin wires that merged into thicker wires, trailing out from under his shirt like they had been attached underneath. Tucked inside his ribcage, right by his soul, was it _in_ his soul? It couldn’t be, it couldn’t … but maybe it could, Sans didn’t know, he didn’t know anything, all he knew was that this wasn’t his Gaster but it _was_ his Gaster and the S.E. was right here in front of him, bright and burning and those wires were linked to the Core, all the energy of the Core pouring into it, far more than had ever been in the machine and it was …

It was … merging them.

All of them.

Every single Gaster. Into one.

Like the machine. Existing in all universes as well. It existed in one, it existed in all, it was pulling them together, it was pulling _every Gaster together_ into one and it was doing it with the Core, the whole Core from every universe was being yanked into one single Core and …

Alphys. _Papyrus._

Flickering.

Flickering like Gaster, but _stronger,_ like they couldn’t control it, they didn’t have the S.E., not like Sans did, he was stubborn enough, stubborn like the machine, he could stay _himself,_ and so could all the others in all those other universes, staying themselves even as they were yanked into this place, but not everyone else. The closer they got to Gaster …

The closer they got to the _source of the S.E. …_

The more it tried to yank them together.

Tried to bring together all the different versions from all the different universes all at once.

But they couldn’t coexist. They weren’t strong enough, they weren’t _stubborn_ enough, they couldn’t take it, they couldn’t merge like Gaster, they couldn’t stay themselves like Sans, so they would …

 _Gaster_ was …

“why?” he breathed, and it didn’t matter that Gaster couldn’t hear him, it didn’t matter that the alarm was still blazing, deafening, nothing mattered as he stared up at the twisted amalgamation looking back at him with a thousand eyes shoved into two empty sockets. “what the _hell_ are you trying to _do?!_ _”_

“E͇ve̹̮̖̻͓͢r͓̝̜̥ỵ̨̭͚̩͚w̪̻̤͍͔h̰̣͟ͅȩ͕̞͔͕̲r̳͎e͚̺̻,” the not-Gaster said, and it was the same voice, the same combination of far too many voices, distant and lifeless and yet painfully familiar. “Don’t need to go to all the other universes, can’t, don't h-have to, can take all the souls, only need seven, seven souls just reach out and take them and break the barrier, break all the barriers, go to the surface all the barriers broken all monsters free no more humans can’t reset can’t come here can’t hurt us no humans just us safe forever.”

Sans’s head wasn’t working. None of this made sense, none of this should be happening, none of this made _any goddamn sense and he just wanted to go home but he didn’t even know if he could anymore_ —

“you’re gonna _kill everyone!_ don’t you see what this is doing?!” he spat, throwing his arms out to his sides and letting the alarm and the shaking metal of the Core and his own shivering breath reach him at last.

Gaster looked … confused. Was that what confused looked like on this face? On every face of every Gaster in every universe?

“You wanted this,” he said, as much to himself as to Sans. “Wanted this. Didn’t want to steal, no stealing, bring them all together, only one, only needs to be one, humans broke our worlds into thousands but we only need one take all of the best and put it into one world.”

Sans wanted to clamp his hands over the sides of his head to keep the voice from echoing, bouncing around the insides of his skull like the time Papyrus had dropped a bouncy ball in his eye socket when he was lying down and it took their dad an hour to fish it out because Sans didn’t want to stop squirming and rolling it around. But Gaster was still talking, he wouldn’t stop talking, was his voice getting louder, it was like every version of him was screaming and it was all Sans could hear and it _wouldn’t stop_ —

“The humans can’t stop us. Not strong enough. Souls and the Core and the S.—deter—can’t kill us all all of us together we’ll stop them we’ll fight like we wouldn’t fight before—”

“you’re _insane_! ” Sans burst out, stamping his foot down hard enough to make the catwalk tremble beneath him. His breath came in huffs, his fists trembled, his left eye flickered with color as his magic bubbled and flared. “you’re putting this whole _universe_ in danger, maybe _every_ universe! you think you’re _helping?_ all you’re doing is screwing everything up, that’s all you’ve done for months, just ruin every good thing we have, you took away everything i loved, you ruined my _life, you killed my bro—_ ”

“SANS?”

Sans froze.

The voice was distant, faint, strained, but Sans would know that voice if it had been garbled ten times over and spat back out backwards. It echoed around his head as he finally noticed the sound of clanking footsteps against metal, louder and closer by the second.

“SANS!”

No. No no no no _no._ He couldn’t be here. Not now. He couldn’t see this.

He turned around.

And he saw Papyrus, clutching his head, flickering twice as hard as before, he could barely keep his eyes open, he could barely _stand_ but he was walking, stumbling toward him, powering through what looked like agony, just to reach his brother.

“papyrus,” Sans breathed, barely loud enough for even him to hear over the alarm, and Papyrus kept moving, trying to look at him, glancing around just enough not to fall over the edge of the floor. Sans jerked his head between his brother and Gaster, his breath coming so fast it made his ribcage hurt. “papyrus, go, get out of here, it’s not safe!”

Papyrus shook his head without looking up, biting back an obvious whimper before peering out at him through tight sockets.

“I CAN’T LET YOU—Sans—can’t do this by yourself, have to keep you s-sa͜fe̴—my brother, too—BROTHER—”

And Sans’s breath stopped.

Because that was Papyrus’s voice.

That was _Papyrus’s voice._

But … but it couldn’t … it wasn’t, it … he was dead he could still feel his dust on his shirt he had watched him crumble in his hands felt the last of the magic leave his soul he _couldn’t but he was he_ —

He shook his head, shook away the thoughts, held his hands out in warning, motioning him back, can’t get any closer, have to get out, stay safe, get _away._ “pap, you can’t stay here, get out, i’ll be out soon, just—”

“DAD?”

Papyrus wasn’t looking at him.

He was looking behind him.

At the man standing in the middle of the catwalk.

Staring at him despite the pain, despite the effort, locked on him like he was … familiar.

Sans shook his head, eyes growing wider still.

“but you … you don’t …”

“DAd …?” Papyrus repeated, as if he hadn’t heard Sans speak at all, and Sans knew that voice, he had heard that voice every day of his life, reassuring him, comforting him, encouraging him, always there, right beside him until Sans screwed everything up and he was _gone_ and he _couldn’t be here_ but—

“Papyrus.”

Sans whirled around, blinking as the voice echoed over and over again, but it was just one voice this time, one voice even though when Sans turned around he was still flickering, still hundreds, thousands at once, staring at them with a faint light growing in his empty sockets.

“Papyrus,” he repeated, and all the voices were back but they were different now, softer. “Gentle. Kind. Creative, innovative, sees the whole world a different way, not like me, not like Sans, never saw all you could do, why couldn’t I see, right there in front of me, amazing, unique, no one can see it I can see it never appreciated it then you were gone gone not-gone never gone always here have to keep you with me love you so much it hurts I … I …”

He froze, his mouth hanging open before he brought it carefully shut, the lights in his eyes growing and dying so fast Sans almost couldn’t make them out.

“Have to keep you safe. Protect you. H̚ä́͡v̓̅͒ͨͨėͬͪͣ͊̚͠ ̂ͥ̈͡to … have to get you out of here. Doesn’t matter how, doesn’t matter who gets hurt, have to get you out, you can see the world, you deserve the world, I let them take the world from you won’t let them take it again even if I hurt you even if it’s the only way I have to no n̵̳̜̻ͣͦͭͥ͜o̲̞̺̹̣͆͆̓̋ can’t hurt them not worth it never worth it screaming crying begging stop hurting them love them can’t hurt them but it’s the only way they’re our ticket out of here that’s what I made them for to get us out no no no love them wanted them sons my sons they’re all that matters have to be a good dad can never be a good dad but have to try doesn’t matter how I do it nothing matters … none of it’s real … just in a head, not my head, none of our heads, just … numbers, numbers in a m̧͙̙͠a̮͇̩͍̩c̵͉̬̤̭ͅh̵̞͟į̬̱͚̳͎̮̦̟n̼̟͞͞e̲̦, programs, he wrote us, made us, copied us, controlled us, made me era̡̱̼͍͎͔͉̠s̴͔͓̻͞e̗̥͖͚̤̬͝d̵̩͍̺̤̙͇̖͔̭͘ me let them hurt you over and over nothing I can do nothing matters they control us they control everything their choices not ours never ours just _theirs_ …”

The words resonated even after Gaster’s voice stopped. He flickered again, like a glitch, like a computer screen, like his body was in three places at once, trying to pull itself back together, the image of him freezing before moving again.

“Someone’s there,” he whispered, but somehow it was as loud as before. “Always there, always w̯̣͓̟a̬̻t̙̲̳̜̜̹̬c͠h̤̜̝̻̺̻͉i̳͇n̶͇̗̼͔̦̰g̞ … made us, made us to destroy us, everyone lives, everyone dies, it all ends, everything ends, doesn’t matter, none of it matters, it’s not real … none of it is real, it’s all just a g̡̢͚̱̳̥̱̞̟̦̮̕͡͠-̧͟҉̶͖̫̞̯͓͈̙̼̞̦̳̣̮̝g͝͏̸̤̘͎͕-̴͎͖̙͓̗͎͜ͅg̛̞͎̪̝̞͜͢-̸̩̘̜̜̠̺̤̹͔̯̟̠̙͔̱͝ģ͓̪͇̯̕͞-̵̧͇̻͍̞̤̩̤̦̖̬͈͖̗̮͚̼g͏̶̶͕̤̠͎̙͚̣͇͎͔̻̮̩̕͝ą͢͏͈̬̦͍̞̲̩̰͉̞̗̥̤̰̤m̫̜̝̞̯͉̯̟͙̺͖͍͕̰ḙ̡̧̢̳̜̦—”

“ _dad_! ”

The word tore itself from Sans’s throat like it had been yanked out, and Sans stood there, panting, frozen, as Gaster’s eyes locked on something in the distance before falling onto him, the lights within them burning to life and settling on his own.

“… Sans.”

Sans couldn’t breathe.

That was … that was his name, Gaster had said his name before, but this was …

It was different. No one said his name like that, only _one person in all his life_ said his name like that.

Sans looked up at him. Just looked, and found him staring back at him, a faint glow deep in his sockets as his head tilted to the side.

“The little one. Little one with the bad eye,” he went on, his voice stuttering, rising and falling, breaking and coming back together, like errant lines of code. He shook his head, his browbone creasing in distress. “I caused it, my fault, my bad genes—”

His voice cut off, and for a second, he flickered again between a thousand different versions of himself, every version, every Gaster that had _ever_ existed. His hands trembled as he held them up close to his torso, and his eyes, glowing once more, fell on Sans again.

“He’s perfect, just the way he is, we’ll make it work, he’s precious, both of them are precious …”

His gaze drifted from one to the other, to Sans, then over Sans’s shoulder to the skeleton who now stood only a few feet away.

“Papyrus,” he breathed, with such affection, such love, that it made Sans’s whole being ache. “Sans …”

Sans’s throat tightened until he could barely manage a sound. “dad …?”

Papyrus whimpered behind him, his body still flashing, in and out, back and forth, not sure if it wanted to exist or not. Gaster’s eyes flicked back to him, and for a few seconds, his form seemed to hold.

“I made you. You were … my bone. You were … it was an accident, but … it was the best accident. The best experiment I’d ever done, the experiment that never ends, see if I can do it, see if I can take care of them, can I be their father, they deserve better, they deserve everything, but I can’t let them go …”

He breathed, and it was a real breath, one person breathing, in and out, just one, even though he flickered as soon as it was done.

“They’re … e͘ve̛ryt̶hing.”

Sans’s hands trembled so hard he was afraid they might fall off his wrists. Gaster looked to him again, and Sans swore he saw tears at the corners of his sockets, even though they disappeared every few seconds, fading and returning with the rest of his expression.

“Sans. Sans,” he murmured, his voice like a whine, desperate and distant and young and so, so old. “Hurt them. Hurt them so much. I hurt you so much, Sans. I hurt you both, over and over, so many different—”

“dad,” Sans breathed, like it was being ripped out of his throat, his dad, his _dad,_ he was there, looking at him, he was so different but those eyes never changed, those were his _dad’s_ eyes, so kind and gentle and loving and it was him, he was still there, he had never left, he would always be there, he would _always be there_ —

He was shaking his head, his mouth barely parted, his eyes drawn so wide they barely fit on his face.

“All the different worlds, how many times did I mess it up, how many times did I ruin it, how many times—I didn’t have you, how many times I lost you, I can—I can’t ever keep you, I want to keep you both, more than anything, I just want you to stay with me, see who you become, see who you _are,_ you’re …”

There was still noise coming out of his mouth, but it was like gibberish, like faint whispering of a thousand different people at once, and it should have been terrifying but instead it just _hurt._

“Dad …” Papyrus murmured, and it was like a whimper and a whine as he tried to lift his head and look at him but he was hurting, he was still hurting, Sans reached for him and grabbed his shoulders and held him upright, supporting him, he had to get him out of here, get him away from all this, but he _couldn’t move._

Couldn’t help.

Couldn’t do anything.

He could _never do anything._

“My children,” Gaster breathed, and Sans couldn’t tell if he was even breathing any more, couldn’t tell if he was talking to them or something else, his body solidifying for a few seconds before it began to flicker again. His breath-that-wasn’t-breath hitched, and it was like listening to the suppressed sobs of a thousand people at once. “ _Mỵ̮͚͙͡_ children. I …”

Sans’s hands trembled, gripping Papyrus’s arms as tears slid down his cheeks. When had he started crying? When had he …? It didn’t matter. Nothing mattered. His dad was here, looking at him, shaking his head, and those eyes, he _knew_ those eyes, the eyes that had looked down at him and his brother when he told them a story before bed, as he held them, as he cradled them and kissed their heads and carried them back after a long day at the lab and—

“You deserve everything,” his dad said, his voice so soft, as soft as it had been as he looked into Sans’s eyes and told him how proud he was, he had come so far, he would go so far, he was going to do amazing things, he—“Everything in the world. And I can’t give it to you. I took it all away, I ruined it, I—”

“no,” Sans cut him off, his voice choked off by the tears forcing their way up his throat. He gripped Papyrus tighter, feeling him flicker and fade, clinging to him with his hands as he clung to Gaster with his eyes, never let them go, too precious, never let them go. “no, we can still … we can go back, we can fix it, we can all be together, you’re … you’re better now, you won’t hurt us, we love you, i love you, dad, just … just stop it and come back, okay?”

His dad looked at him. Just looked at him. He was flickering harder now, he was himself, he was a hundred others, he was all of them and none of them and Sans squeezed Papyrus so tight it must have hurt, he could barely breathe past the tears clenching his throat, but he never looked away.

“Go back,” his dad repeated, his voice vague and faraway. “Go back to how things …”

He trailed off. Sans wanted to shout at him, scream to hurry, let’s just get out of here, everything was fine, everything _would be fine,_ they would fix the machine, they could figure it out if they all worked together, and even if they didn’t, even if they were stuck here for the rest of their lives, at least they would have—

“We l̤̭̠̩̱̰o̼͈͉v̞ed you,” his dad said, and it wasn’t just him, it was a thousand voices, identical, all speaking at once. “We all loved you. Every time you existed, every time, sometimes we ruined it, right from the beginning, but the second we saw you, we loved you both. More than anything.”

His eyes drifted from Sans to Papyrus, back and forth between them, and Sans found his own gaze following, down to his brother, his face still clenched in pain but his eyes open, staring back, so young, so old, so more much than Sans would ever deserve, everything he had lost, everything he could _never lose again._

“We wanted everything for you.”

Sans couldn’t breathe. He wanted to grab both of them and run, he wanted to get out of here, he just wanted to go somewhere safe, even if it wasn’t home, he would _make_ it home, as long as he had both of them, as long as he had his dad and his brother, everything would be alright.

“Instead we took it all away.”

It didn’t matter. None of it mattered, he would forget it all, pretend it never happened, they could go on like before, they would heal, they would pretend, they would live and be happy and maybe this Papyrus wasn’t _his_ Papyrus and maybe it was and it _didn’t matter,_ it would all be okay, they would all be okay—

“But we won’t do it again.”

Sans looked up, his eyes bright, his smile wide despite the tears that kept on falling.

“no. it’s over,” he choked out, like a laugh, like a happy, wonderful laugh. “it’ll be okay now, yeah? you remember us. you remember that you … you won’t hurt us. i know that, pap knows that, we—”

Papyrus jolted, and Sans squeezed him, turning just in time to see his brother flickering harder, his eyes squeezed shut, whimpers slipping past his teeth. Every few seconds, Sans swore he wasn’t even there anymore, he was disappearing, fading, in and out, away, away—

“pap!” He grabbed his shoulders, held him close, no, no no no, they were getting out, it was gonna be fine, he wouldn’t lose him again, no matter what it took, he _couldn’t_ lose him again.

“Horrible things. We’ve done horrible things. So many … ruined it so many times … not again,” Gaster went on, his eyes locked on Papyrus now, taking him in, looking at him, really looking at him, seeing everything Sans had seen from the beginning, everything he had begged his dad to see every time he missed what was right in front of him. “Can’t go b̫a͚̟̣͔̺c̺͙̹̖̲͈̻͟k̥̯͕̲̞̞̮.”

He turned to Sans, and for a second, just one more second, it was him. It was his dad. Completely his dad, _only_ his dad, the dad who had held him and laughed with him and made terrible puns and encouraged him and wrapped his arms around him and told him he could do anything he put his mind to.

“But we can fix it.”

Sans’s breath sped up. He looked to Papyrus, shivering so hard his bones had begun to rattle. He looked to his dad, browbone furrowed, shaking his head.

“dad, what are you talking about? just … come on, get rid of that thing and let’s go. we’ll be fine, all three of us, together.”

“I can’t get rid of it, Sans,” his dad said, more calmly than he had said anything in his entire life.

“what the hell are you talking about?” Sans spat, gesturing with his free arm toward the man in front of him, unable to make out where the S.E. core ended and his dad began, unsure where all the other versions of his dad began and ended, unsure who even _was_ his dad as he flickered too fast to see. “just … just get rid of it!”

“I can’t,” his dad repeated, why did he sound so calm, like it was fact, like he had _accepted_ it, he hadn’t accepted that they couldn’t break the barrier, he hadn’t accepted that Papyrus was dead, but he was just going to accept _this_? “Can’t separate us. I know them now. I am them. All of them. We all exist together. Just one. No more. Never more a̝̻̲͔͖͍͓g̬̦̱͇a̬̳͓̞̹̫̞ị̜̝̩͖̦̫n̦͔̲̬̤̜.”

The other voices melded with his every few seconds, and it sounded like a thousand people were talking at once, a thousand people with the same voice, quiet yet infinitely loud at the same time. Sans shuddered against his will, swallowed, and shook his head.

“okay, we … we’ll find a way. i’ll help you. we’ll figure out a way to get it out of you.”

“There’s no time,” his dad went on, and he was calm, he was _so fucking calm,_ but there was urgency now, something that screamed like a timer close to going off.

Papyrus whimpered at Sans’s side, louder now, like he wanted to cry out but held himself back. His sockets squeezed shut, his body trembled so hard Sans could feel his own bones beginning to shake in sympathy, Sans held him tighter, just a little longer, Pap, he’d get them out of there, he just needed to … to …

“then … just disconnect the power,” he managed, his voice weaker than he would have liked. “that’s what’s strengthening it, right? it wasn’t doing this before, you just need to disconnect yourself from the core and—”

“I know you never spent much time in electrical engineering, Sans, but you must know that this much power doesn’t just stop flowing,” Gaster cut him off, and goddamnit, why did he look so fond, why was he _smiling_? “It has to have somewhere to go.”

Sans’s breath sped up, and he shook his head, again and again as each idea popped into his mind only to be shooed away when he realized how ridiculous it was. “we’ll—we’ll think of something, we made a machine that travels across _universes,_ we can fix a damn electrical system!”

“You know it’s not that simple, Sans,” his dad said. And it was his dad, _just_ his dad, barely louder than a whisper, but even above the sound of the alarm and the trembling metal and Papyrus’s muffled cries, Sans heard it like a shout.

He bit back the whine growing in the back of his throat.

“there has to be something, there’s _always_ something!”

His dad looked at him, so gentle, so loving, his eyes flicked between the two of them with so much affection and care that Sans swore they were just babies again, held in their father’s arms, cradled and treasured and it didn’t matter that his dad had no idea what he was doing, because he would always _try._

“Perhaps there is,” he breathed, a smile curling the corners of his mouth. “Perhaps you’ll figure it out. But I won’t be here to see it.”

“stop it,” Sans snapped.

Gaster didn’t react, just shook his head. “Nothing will stabilize as long as I am here.”

“no,” Sans choked, squeezing Papyrus tighter even as he struggled to stand under the weight of them both, his legs shaking, his whole body shaking, the building around them trembling with the strain of the power coursing through it. It wasn’t made to sustain this, it wouldn’t hold much longer, they had to go, but he couldn’t he couldn’t _no._ “no, no, _no,_ don’t you _dare_ say that. don’t you dare. you’re not a quitter, that was what i told you, didn’t i, you never quit, you can _not_ quit now!”

“I’m not quitting. I’m keeping you safe,” his dad replied, as if it were the simplest thing in the world. “I̬͍̝͔͔͍͇͓͠ we want you safe. Always want you safe.”

Sans choked on a sob in his throat and shook his head again.

“not like this. it’s not _worth_ it.”

“You’re worth everything,” his dad said. And it _was_ the simplest thing in the world. In his eyes, in the eyes of every version of him who stared at him now, it was the only thing that mattered. “Destroy the S.E. core.”

Tears dripped off the edges of Sans’s jawline, he couldn’t breathe, he couldn’t move except to shake his head, harder and harder, his browbone firm and his arms so tight around Papyrus he must have been hurting him.

“no,” he bit out. “i won’t do it. i'm not gonna kill you!”

His dad’s eyes shone with something like pain. Papyrus whimpered, and Sans and his dad turned to him as one as he forced his eyes open, just enough to look back at them, to look at their dad and he knew him, he _knew_ him, this was their Papyrus, this was …

“Dad …” Papyrus whimpered. Like a plea.

And his dad looked back at him with all the pain Sans had wanted to see on his face every time he strapped him to a table, all the love, all the concern, every ounce of affection he had held back for months.

Then he turned to Sans again, more desperate than before. “He’s worth more than me, Sans. Your brother’s worth more than saving me, saving _everyone_ is worth more than saving me.”

Sans could barely see through the tears blurring his vision. He tried to lift his hand to wipe them away, but his hand kept shaking and he couldn’t let go of Papyrus and all he could do was stand there and shake his head because he was right, his dad was right, but it didn’t change it, it didn’t change the love and care in his eyes right now, it didn’t change the fact that he was _there_ when he had been gone for so long and Sans couldn’t lose him again, not again, _not again_ —

“i … i c—”

His voice died in his throat. His dad looked at him, then let out a long sigh that trembled as a thousand others matched it. There was no anger. No disappointment. There was just sadness glowing in two mismatched sockets, and it hurt worse than anything he could have said.

“I love you,” he whispered, like a scream over the sounds overpowering them. “I love you both so much.”

It sounded so warm, so comfortable, and Sans swore he could imagine a gentle hand smoothing over his skull, tucking him into bed and never saying no if Sans or Papyrus asked him to stay until they fell asleep. The voice of his dad as he fussed over the slightest injury, as he held him close, as he told him that no matter what, everything was going to be alright.

His eyes softened further.

“But sometimes, you have to know when to quit.”

Sans almost didn’t notice his dad’s feet shifting, moving him in slow, careful, uncertain steps toward the edge of the catwalk, only a few feet away. Every movement made him wobble, like he had to convince every version of him to move before he so much as shifted, but he was moving, he was _walking_.

Toward the edge.

“no,” Sans managed, everything was burning and he didn’t want to be here, he just wanted to go home with his brother and his dad and pretend this had all been a dream, and Papyrus was shaking next to him and whimpering and he was hurting, flickering in and out like his dad was but his dad could take it, Papyrus would … Papyrus would … He stepped forward, reaching out a hand. His dad stopped, and Sans shook his head. “ _no._ i can’t. i-i …”

“P̵̱̥̫͉̩̝͢l̡̲̣̬͇̬̮̗ȩ̷̮̩͇̱̦̟ͅa̢͙͓̞̳s̡̮͓̲̯͎e͉͕̜͔̝̯͟, Sans,” his dad breathed, and his eyes were on Papyrus now, soft and aching and desperate. He took another step. Sans’s hand shook, Papyrus whined and pressed closer to him, but Sans kept shaking his head, stepping forward, reaching out his hand, forming the magic around it, he could grab him, he could pull him back, they could leave together, they could find a way, they _had_ to find a way, he couldn’t let him die, he couldn’t lose his brother but he couldn’t lose his dad and he _couldn’t lose anyone else._

His dad’s eyes shone with something like tears, but Sans just gritted his teeth and held his brother tighter, as if in an apology he might never understand.

“i ca—”

Then he saw him.

Just a flash of white, accompanied by thudding footsteps echoing over the metal floor.

A flash of white in a gray hoodie.

The other Sans slammed into his dad’s side, throwing him off balance and sending him tumbling over.

Over the edge of the catwalk.

Careening toward the lava below.

Sans couldn’t even scream. His arm hovered in the air, reached out, he struggled to focus his magic, but he managed it, reached, reached, stretched, but …

There were too many.

Too many.

Hundreds, _thousands._

All in one.

Every single soul belonging to every single version in every universe in existence.

And Sans couldn’t grab them all.

His dad’s feet left the catwalk, stumbling out into thin air, and the other Sans fell with him, his eyes locked on Sans, sockets empty and sharp, burning, his smile tight and desperate and sad and then he wasn’t looking at him, he was looking at Papyrus, _his_ Papyrus, _their_ Papyrus, and he was pleading, without saying a single word, _keep him safe._

They fell.

Down.

Down.

D o w̷̢͉̠̤͚̱̺ ̴̝̘͢n̢̨̛̙͔̰̰͈̜̲ …

Sans threw himself forward, scrambling to grab the cord still latched onto his dad, he could still pull him back, he could stop it, he—

Arms wrapped around his waist and yanked him back.

Something hit the lava.

The Core jerked, taut, buzzing with a current so strong Sans swore he could see it, the connection severed, the power surging, one final burst, Papyrus held him tight as he screamed and thrashed and reached out for someone who was already gone.

Then the current stopped.

The alarm seized.

The building stilled.

And Sans slipped into darkness.

**Notes for the Chapter:**

> For those of you who might pick up the similarities between this chapter and The Scientist, believe it or not, I had actually planned this whole thing out before I read it! But still, I acknowledge the similarities and if you haven't read [The Scientist](http://archiveofourown.org/works/5301182/chapters/12238256), you definitely should.
> 
> Also, this story is far from over. There's one chapter left in this fic, but there's still a short story collection and two full-length sequels to go after that. So stayed tuned. ;)


	52. Chapter 43

Sans didn’t remember how he got back to Alphys’s house.

He was standing there, looking down into the lava around the Core, and then he was in a bed, staring up at the ceiling. For at least ten minutes, he had just lain there, not moving, just looking ahead of him, before the door opened to his left and Papyrus stepped into Alphys’s guest bedroom, shouting at him to stop being a lazybones and get out of bed before he wasted away the entire day.

It took him another five minutes to bring himself to push the covers off his body and walk through the house toward the kitchen.

For more than an hour, he still wasn’t sure what was happening. What had happened. Like he had put up a wall in his head so he didn’t have to think about it. And he didn’t. He sat at the table in complete silence, watching as Alphys set out plates of the breakfast she had cooked—or stuck in the microwave, based on the empty frozen meal boxes he saw sticking out of the trash can. He watched Papyrus chat away with Alphys like he had so many times when they had been kids, even though the two of them had never shared many interests.

He had always admired her, even if he couldn’t understand half the words that came out of her mouth sometimes.

And she had always adored him, treasured him like a little brother even when they were basically colleagues.

It took him a long, long time to remember that they hadn’t known each other at all until yesterday.

He didn’t remember what was so important about that until he was sitting on Alphys’s couch, curled up next to the arm, watching anime on her TV, and Alphys’s phone rang.

He couldn’t hear the other side of the conversation, aside from the vague sound of babbling. He thought he recognized the voice: feminine, loud, rather grating. Alphys didn’t use their name. But he could hear Alphys just fine, responding to questions.

Questions about the Core.

Questions about a major malfunction the previous evening that had shaken the entire Underground, hard enough to break some “all the new plates I bought to replace the ones I broke,” from what he could make out.

Sans sat there for a moment, staring at Alphys, at her phone, at Papyrus sitting at his side.

Then he remembered.

He thought, for a second, that he was going to die.

He was hot and cold even though he _couldn’t_ be truly hot or cold, he couldn’t breathe and suddenly he swore he _needed_ to breathe, he couldn’t move, he couldn’t think, all he could do was stare in front of him and see the faded skeletal form falling toward the bubbling lava below.

Papyrus’s arms around him, tugging him away from the edge as he tried to approach it.

The sizzle as a body hit the lava.

Then nothing.

Nothing.

_Nothing._

Dark, darker yet—

“SANS?”

Sans jerked his head up, blinking when he found both Papyrus and Alphys staring at him with wide, concerned eyes. Alphys had set down her phone, apparently done with her conversation. Papyrus watched him for a second before coming to sit on the arm of the couch next to Sans. He put a hand on Sans’s cheekbone, and his hand was real, it was here, it was his brother but it _wasn’t_ his brother and it didn’t matter because he was here and Sans wanted to cling to him he was alive he was here and their dad was—

“SANS, WHY ARE YOU CRYING?”

Sans blinked. Then he blinked again, and finally he felt the wetness seeping out of his eyesockets, flowing over his cheekbones, choking him, smothering him, Papyrus was looking at him and he still couldn’t move, he still couldn’t breathe, but Papyrus was here, Papyrus was _here,_ and it was the wrong one but it didn’t matter and then both Papyrus’s hands were on his face, holding him tight for several long seconds before he let go and slid his arms around his back, pulling him into a tight hug.

“IT’S OKAY, BROTHER,” Papyrus whispered, somehow still sounding like a shout. His fingers brushed over Sans’s skull, his other hand pressed firmly into his back. “I … I DON’T KNOW WHAT’S WRONG, BUT WHATEVER IT IS, IT’S ALL GOING TO BE OKAY.”

Sans choked on a sob, but swallowed it back before it could slip past his teeth. He lifted one hand to cling to Papyrus’s shirt.

His voice refused to work. But no more tears came.

At some point, Alphys left the room, murmuring something about going to work, but Sans didn’t even look up. He just sat there, leaning awkwardly over the edge of the couch, clinging to Papyrus and feeling the thrum of the soul, the one solid, familiar thing, as the rest of his world crumbled away.

*

He spent three weeks straight working on the machine.

Alphys gave him parts, even though she didn’t seem to understand what they were for. She helped him look over the blueprints, though it seemed every time she did, she had less and less of an idea of what they were fixing. She helped without compensation, without explanation. He tried to thank her, in little ways. Finding new manga for her at the dump. Giving her the blueprints to the S.E. extractor when she found them in a drawer and asked if she could look them over. But he knew none of it was enough to repay her, even though she would never say so herself.

One day, two weeks in, he asked her to help him work on the machine, and she just looked at him as if he had started spouting gibberish, and asked him if he had started a new project without telling her.

He didn’t ask after that.

There was something in her eyes, something faint and clouded and hidden deep down, that he didn’t want to see again.

He didn’t talk about the machine around Papyrus, and Papyrus never asked.

One day, Sans woke up and went through half his day before he remembered the machine. It came slowly at first, like a fading memory, before it hit him like a pile of bricks collapsing on his head—or the ceiling of a cave falling on top of him. He found himself in Waterfall without thinking, without moving, just flashed in and out of existence and found himself standing right in front of the door to his lab. He opened it.

And there it was. The machine. Untouched, just as he had left it the night before.

He started going to bed with sticky notes on his forehead, reminding him of what he was supposed to do.

Of what he couldn’t forget.

When he found himself knocking the sticky notes off in his sleep, or first thing when he woke up, he found other ways. Little things. Sleeping in his hoodie and “forgetting” to wash it for as long as possible, so it would be the first thing he felt when he woke up, so that he could still make out the scents of the lab and Dr. Japer’s warm fur, even as other scents almost covered them up.

When Papyrus finally snatched the hoodie off of him and scrubbed it clean, Sans started making puns.

Puns and bad jokes. Several times a day. Then several times an hour.

It felt wrong at first. It felt like stealing something that wasn’t his. It felt like taking something off of a dead person.

He heard his dad laughing in his head after every one left his mouth, and it was like having his soul ripped out of his body and torn in two.

He did it anyway.

Papyrus groaned and rolled his eyes, but sometimes, Sans could see him hiding a smile.

It didn’t take long for Sans to make jokes in the hopes of getting that smile, just for a second, without even a thought for where he had gotten the jokes from in the first place.

The first time he heard Papyrus make a pun himself, it took him five minutes to feel the ache in his chest, and another five to realize where it had come from.

He kept making puns. Papyrus kept groaning, and making more of his own.

Sans stopped hearing his dad’s voice in the back of his head.

After the first week, he found an inn in Snowdin that would take him and Papyrus in if he did work for them in the evenings. Alphys had offered to let them stay for longer, as long as they needed, but he had declined. He knew she liked her privacy, even if she seemed to view them as pleasant company. And it had felt wrong to stay, as badly as he wanted to hold on to one more piece of a life that felt so far away.

Papyrus never asked about the machine, and Sans never brought it up. He kept working on it whenever he could, but after the first three weeks, he let himself slow down, just a little, spending time with Papyrus rather than going straight to the lab when he woke up, and Papyrus seemed to accept the excuse that he was “going to get some work done” when he finally left the inn. But Sans did mention Alphys, one month after their arrival here, on a whim, when he was tired from working on the machine and working in the inn and wasn’t thinking about the questions it could lead to.

But Papyrus just stared at him for a long moment before asking who Alphys was.

Sans had to take a minute of silence before he could bring himself to say it didn’t matter.

He tried, sometimes, to figure out what Papyrus knew and what he had forgotten. But Papyrus didn’t talk about his past: the one he shared with Sans or the one Sans would probably never fully understand. He liked puzzles. He liked bone-themed things.

He liked Undyne, the Royal Guardsperson who had tried so hard to get all of them out of the Core.

She didn’t seem to remember much about that night, if anything, but she never complained when Papyrus followed her around, and when Sans watched the two of them talking, they chatted away like they had known each other for years.

He never asked Papyrus how they knew each other. The way Papyrus talked about her, they had been friends for most of their lives, and if Undyne didn’t protest that notion, Sans wasn’t going to either.

Sometimes Sans wondered whether his Papyrus would have been happier if she had been in their universe, too.

Either way, she made him happy here, and that was more than enough for Sans to want to keep her around.

They settled into a routine, soon enough. Sans worked in the inn in the mornings and evenings—far less than was really fair, considering they were getting room and board for nothing else—and went to work on the machine for several hours during the day. He never asked Papyrus what he did during the day, but he suspected that he had taken up cleaning around the inn. Maybe that was why the innkeeper never complained about them staying, despite Sans not doing nearly enough work to pay for their rent.

Papyrus tried to help cook once, but it only took five minutes for the innkeeper to shoo him out of the kitchen and insist that he stick to cleaning.

He was good at cleaning.

Apparently that had carried across both universes.

After the second month came and went, the routine became so, well, _routine_ that Sans had trouble remembering when things had been different. He would go days at a time working on the machine without thinking about _why_ he was working on the machine, tinkering with the wires while he considered funny jokes to tell Papyrus when he got home and what the innkeeper would be making for dinner. Then, without warning, it would all hit him, and he would sit there staring at the hunk of metal in front of him with dark sockets and shaking hands until the alarm on his phone went off and reminded him that it was time to go.

Maybe the normalcy of it all was why it took him so long to realize the obvious.

He had been working on the machine all this time with the hopes that he could regain everything he had lost. He could fix his mistakes, he could get back his home, his friends, his family.

He hadn’t considered the fact that his family was gone.

If he got back to his own universe, all he would find of Papyrus, _his_ Papyrus, his _brother,_ would be a pile of dust. He didn’t even know where the dust was, the dust that hadn’t clung to his jacket and been scrubbed off by another Papyrus, _god,_ he had scrubbed off the dust of another version of himself and he would never know but it made Sans wish he had the parts to be sick.

His brother was dead. It didn’t matter if he got back or not, whether he was here or there his brother would still be dead.

But this Papyrus … he still had a home to go back to, didn’t he? His Sans was dead, but he still had Undyne, and … and Sans didn’t even know, maybe he had plenty of other people to go back to, Sans had to at least _try,_ he had to, he …

But …

But …

What if he couldn’t fix it?

What if he told Papyrus that this wasn’t his world … that he had been kidnapped, that the Undyne he was best friends with wasn’t _his_ Undyne, that his real brother was _dead_ … and the machine was never fixed?

What if it shattered the thin veil of happiness he seemed to have found here?

What if they were stuck here forever, and Papyrus spent the rest of his life yearning for something he could never get back?

Was it more cruel to lie, or tell the truth and risk ruining the rest of his life?

Because he could never give Papyrus back what he had lost. Not all of it. His brother was gone, just like Sans’s Papyrus. No machine could ever bring him back.

And Sans’s dad …

His dad was dead. His version was gone, gone forever, and in all the other universes …

But that had _been_ all the other universes, hadn’t it? All of them. At once. All of them combined into one. Every single version of his dad from every single universe.

And they had all fallen into the Core.

They had all been turned to dust, likely only seconds after they hit the lava.

Even if he fixed the machine … even if he made it back to his own universe, even if he made it back to _any_ of those universes, even if he went back to that world with the rain and he and his brother were together and happy and everyone was living in peace with the humans …

His dad wouldn’t be there.

His dad didn’t exist.

And for all he knew, he was the only person in existence who still remembered him.

That made him try harder, for a while. To distract himself, maybe. Just to give him something to do. To distract himself from the thought of what he would still have lost—what Papyrus would still have lost—even if he fixed it. But after a few days of coming home to a Papyrus disappointed that he had missed breakfast and dinner, a Papyrus scolding him to cover up the sadness in his eyes when Sans slipped off to bed without even pausing to chat, he knew he couldn’t keep that up. He had put Papyrus second before, far too many times. He wasn’t going to do it again.

He kept going for a few days after that, but he knew it wasn’t going to last. He knew it was over. He looked at the machine, looked at the scribbled blueprints, looked at all the tools and parts he had picked up from the dump and which had been given to him by Alphys.

He was never going to be able to fix it.

It didn’t matter how hard he tried. It didn’t matter what parts he added, or took out, or modified. He could butcher the machine so that he couldn’t even recognize it as what it had once been, and it wouldn’t matter.

Without the S.E. core, it wasn’t going to work.

And even if he found a way to make it work, he wouldn’t get back all that he had lost, any more than Papyrus would get back his brother.

His family was gone. His friends were gone. All he had left was right here.

Once, he might have kept trying anyway. He might have spent every hour of every day trying to find a way to get all of it back, no matter how long it took, no matter how much it hurt him, no matter how much the people around him wanted him to stop. He would have pushed himself onward, seeking a goal he wasn’t even sure was attainable.

But that time felt very far away.

And he had lost far too much seeking an unattainable goal to think that he couldn’t lose it all again.

He pushed himself up from the floor and pushed the blueprints and tools to the side. He stood there, in a mockery of his old lab, and stared at the machine he had spent months tearing apart from its original form, the machine he had spent most of his life admiring from a distance, which now barely resembled what it had once been. The machine that had once been his only hope. The machine that had torn the last bit of that hope away.

Then he turned around, opened the door, shoved his hands in the pockets of his old blue jacket, and started back toward home.

*

Snowdin had been weird at first, after growing up in Hotland, but he had always liked visiting as a kid, and the fact that Papyrus was already so comfortable there only made the transition easier.

It also made it much easier for him to decide where he was going to set up their permanent home.

One nice thing about such a small town with so much wide open space was that there was plenty of room for new residents. Even in Hotland, you needed to get permission from the king before you put up a new building—not like that was very difficult, the king approved almost everything, but still, there _was_ a process to follow. And maybe there was here as well. But no one cared enough to enforce it. Sans found a plot of land that looked good, put up a sign reading “Home of Sans and Papyrus, Coming Soon,” and no one protested.

Then it was just a matter of _building_ the thing.

It was impressive, the amount of people around Snowdin who knew how to build houses. Almost as impressive as the amount of people willing to let him pay for construction work with favors instead of actual gold. It took several months, and Sans never mentioned a thing to Papyrus the entire time they were working. But one day, when they were both heading home from a long day out, Sans led Papyrus past the inn and all the way to the edge of Snowdin, to the little plot of land that had been entirely empty a few months before.

The little plot of land now taken up by a two-story wooden house.

Sans would have built the whole thing with his own two hands just to see that bright, ecstatic smile light up his brother’s face.

They were moved in within two hours, and only part of that was due to the fact that they had almost no possessions of their own.

A few weeks later, when Papyrus was settled in, Sans picked up some supplies and got to work on a small shed around the back of the house. Papyrus noticed it, of course, but he accepted Sans’s explanation of just wanting extra storage space.

He gave him an odd look when Sans installed separate locks on the door, but he said nothing about it.

It wasn’t elegant. But Sans had kept a close eye on the builders when they were working on their house, enough to pick up their techniques, and he managed to install little square tiles over the floor, and drawers in the wall. He wouldn’t need anything else. It wasn’t like he would be using it.

He tried to move the machine on his own at first. He didn’t want anyone else involved, if he could avoid it. But he had never been a particularly strong monster, and even less so now. His dad had helped him move into his Waterfall lab in the first place. After four tries that left him collapsed on the floor, panting, he finally found a few monsters who prided themselves on lifting heavy things, and “challenged” them to carry the machine all the way back to his house.

They didn’t ask questions, and were happy enough when he gave them a handmade “badge” made of construction paper stating they were the strongest around.

The rest of the stuff, he carried himself. The blueprints for the machine. His badge from the lab, already covered in a thin layer of dust.

And the photo album, hidden so far in the back of a drawer that he almost didn’t notice it before he left.

He sorted everything away into the shed behind the house. He allowed himself a few moments to open the album, to glance through the pictures, though he forced himself to turn the page as soon as his chest began to tighten. The tears never came. He wasn’t even sure if he had any left.

Only when he reached the drawing on the last page did he really pause, staring down at the crayon scribble his eight-year-old self had worked so hard on.

He closed it again before his throat could tighten enough to choke him.

He locked the lab up, hid the key in his new bedroom, and did his best to ignore it.

He went about his days. He did his jobs as they came in and searched for new ones. He made time to eat breakfast and dinner with Papyrus, and sometimes lunch, too, if he wasn’t too busy during the day. And every time he found himself wandering toward the shed, key in hand, ready to get to work again on a habit so ingrained it felt like breathing, he closed his eyes, paused, and used every bit of willpower to turn around and leave it be.

It wasn’t until a week later that he passed through Waterfall again, and when he did, he came very close to walking by the old familiar wall without noticing it.

Because there was supposed to be a door there.

And there wasn’t.

He had searched the whole area, every place it possibly could have been, spent two full hours making sure he hadn’t simply forgotten where it was. But it wasn’t there. There was no sign of it, as if it had never been there at all.

And he supposed that made sense.

Because it hadn’t been there before they came, had it? He could never be sure, of course, it wasn’t like there was anyone he could _ask._ But what were the chances that Gaster had built a secondary lab in every single universe they visited? What were the chances that there was already space for the machine to exist in every single universe? The machine itself had been permanent, permanent enough to drag several items in the lab along with it. And now that it was gone, now that the S.E. core _and_ the machine itself had been removed … there was nothing to keep it there. No reason for it to exist.

So after two hours of fruitless searching, Sans gave up and went on his way. His eyes drifted to the wall on his way back, but he didn’t let himself stop.

The door came back from time to time. In the corner of his eye when he passed it. He never tried to open it. He never even looked it at for longer than it took to tell it was there. His burning curiosity had faded.

Because as much as he would have liked to know why the door appeared, he definitely didn’t want to know if there was anything behind it.

He didn’t visit the Core at first. At first, he didn’t plan on _ever_ visiting the Core. It wasn’t like there was a reason for him to. He didn’t know how it had been managed, but apparently the maintenance had been taken over almost seamlessly by other people who had worked in it, and Alphys took care of the rest.

She didn’t spend all her time there, but he figured she would be spending more there soon. There was no Royal Scientist, and there didn’t seem to be plans to pick a new one, but even with memories lost, Alphys was still understood to be one of the most knowledgeable scientists around, and despite her constant anxiety, Sans had no doubt she would step up to fill the gap, title or not.

She didn’t need him. She had never needed him, in any universe, and in this universe, she definitely didn’t. So there was no point in him going back there when it would only make him remember what had happened.

But that was just it. It made him remember.

And on a day when the jokes completely failed, when he found himself forgetting about the machine, when everything he had put together to make sure he _never forgot_ collapsed underneath him, he went to the Core.

He didn’t go very far into it. Not now. He was desperate, but he wasn’t stupid enough to go back to the exact place where it had happened—not that his memory was clear enough to give him all the details anyway. But he wandered around, dismissing any queries as to who he was or what he was doing by saying that he was Dr. Alphys’s colleague. Even if she found out, he doubted she would mind, and technically, he supposed, it was true. Somewhere.

He walked, and tried to make note of all the little differences between this Core and the one he remembered, but he couldn’t remember all the little details because he had never paid much attention to them in his own world, and he couldn’t tell whether this Core was almost identical or completely different and he would never be _able_ to tell because this was the only Core he would ever see now. Would he have spent longer studying it, had he known he would never see it again? Would the Core have even mattered, compared to all the other things he was going to lose?

He wandered for a while, five minutes, thirty minutes, an hour or two, and he had to force himself to turn around and start back toward the exit. As much as this Core might have changed—or not changed—he could at least recognize the general path taking him back toward the exit. In no small part because there were electronic signs every thirty feet or so, pointing him in what he hoped was the right direction.

Sans had almost reached the exit when the Core began to move.

It had happened dozens of times when he had visited the Core in his universe, and he almost didn’t notice it. But after the initial jolt, when the part of the Core on which he stood began to slide around, he stiffened, his eyes shifting from side to side as if to confirm what he was feeling was real.

The Core was moving.

But … this Core wasn’t designed to move.

Papyrus had never created the puzzle method to make it move, because _Papyrus was never born._

Could Gaster have thought of it on his own? Maybe, sure, it wasn’t _impossible_ , but … Gaster didn’t think that way. Not like Papyrus did. Sans had never met anyone who thought quite like Papyrus did. Who could think around a problem like that and come up with the perfect solution that sounded _so silly_ in theory but in practice solved an issue that that stumped Gaster for years. And besides, Alphys had told him about that explosion. The explosion because of overheating. The overheating that the movement had _solved._

Maybe … had the problem been solved after the explosion, in recent years? Before Gaster had …

Or had that changed it?

When all those universes had been yanked together, when Papyrus had been every Papyrus and Sans had seen all those versions of himself and Gaster had been _every Gaster at once_ …

Had it changed the Core?

The movement stopped, and Sans paused only a moment before scurrying forward, rushing out through the exit even though he knew that once the Core moved, it wouldn’t shift again for another two days. He didn’t want to be here. He didn’t want to think about this. He didn’t want to see one more thing that was the same even though it _shouldn’t_ be the same, he didn’t want to be reminded of the Papyrus that had designed the shifting puzzle pieces of the Core because that Papyrus was _gone_ and he was never, ever coming back.

He didn’t notice where his feet were carrying him until he was back in Snowdin. Behind their house. Staring at the door to the shed.

The key already pulled out of his pocket and turning in the lock.

He walked in without a thought, without a second’s hesitation. He closed the door behind him and stood there, right by the entrance, looking at the machine covered up by an old sheet he had found at the dump. It seemed funny now, worrying about dust. But he couldn’t bring himself to just leave it there to rot. Deep down, very deep down, maybe part of him wanted the assurance that should he ever decide to come back, to try again, it would still be there waiting for him.

But he wasn’t trying again.

He _couldn’t_ try again.

He had already decided that, hadn’t he? There was no way he could go back. And even if he could … there were still plenty of things that would be gone.

He wondered, for the first time, if Alphys missed him. If she was worried about him. She had always been so paranoid when he was a kid, afraid she’d lose him, that he’d get hurt and it would be her fault. Even when he had grown up, even when they stood on entirely equal ground, she had never lost that attitude. Toward him or Papyrus.

She was probably worried about Papyrus, too.

He wondered, for a second, whether she had found his dust.

And Dr. Japer. She would be looking for them. And Dr. Frewth, and Dr. Lemming. They would find their house empty. Abandoned. Maybe Alphys would finally check the lab. It wasn’t like Sans had locked it. She had always respected his privacy, but eventually her concern would win her over. She would check the lab, and she would find the machine gone. Because Sans had moved it. Maybe it had moved into Snowdin in that universe, too. Or maybe, without the S.E. core, it would simply cease to exist.

Maybe she would look for it. Or maybe she would ignore it and just search for all of them. For Papyrus, for Sans, for—

But she wouldn’t search for Gaster, would she?

Because if everyone in this universe had forgotten Gaster … if that had been _every single Gaster_ that had fallen into the Core …

She would have forgotten him, too.

Dr. Frewth and Dr. Lemming would have forgotten their colleague. Dr. Japer would have forgotten a friend she had had for more than a hundred years.

And even if Sans managed to make them remember … they would never feel the same way about him as they had before. Not when they knew.

And Papyrus wouldn’t know any of them. Not this version of them. They would remember him, but they would remember the wrong him, and he would have to start his relationships with them all over again, just like he had here.

The world Sans had known, the world he had grown up with, was gone. His friends. His brother.

But … Papyrus was still here.

He was here. And he was settled. He had a _home,_ and it was a good home, a home he was proud of even if Sans couldn’t look at it without thinking of the home he had modeled it after. He decorated his room and kept the whole place clean no matter how often Sans messed it up. He was starting a collection of books, some of them picture books he had collected from the local shopkeeper—Sans had almost passed out when he first found Papyrus holding _Fluffy Bunny_ —and he had picked up a couple of action figures which he insisted he had been collecting for years.

He had a friend. Just one friend, but she was a good friend, a friend who loved him exactly the way he was—even if it wasn’t the same friend he remembered, even if the friend he remembered must be missing him, must think he was dead.

He never mentioned money. He never worried about money, except when he was gathering pocket change to buy something for himself. Sans made it clear that he would take care of putting a roof over their heads, food to eat, earning enough money to live comfortably, even if it wasn’t through a regular paycheck. Papyrus scolded him for plenty of things, for lazing about, for leaving his dirty clothes everywhere, for never doing the dishes, but he never asked Sans about money.

Maybe he had never had to think about money before, in his old universe.

Maybe he just trusted Sans.

Either way, it didn’t come up. Papyrus took care of the housework, keeping everything clean when Sans would have just as easily the house get messy enough to explode, and Sans took up as many odd jobs as he could to take care of the bills. For the first time in his life, Sans didn’t think about big plans, what he was going to be doing in six months, a year, ten. He made money, he spent it. He got the bills, he paid them. He found a job, the job ended, he found another. He kept going, even if some days it was like trying to pull one of his own teeth out with a pair of old tweezers.

And Papyrus was happy.

Happy enough, at least.

He rolled his eyes and groaned when Sans made bad puns. He smiled and laughed when he finished making a puzzle—one of his favorite hobbies. He went about his day like this was all he had ever known, even if he dreamed of something more. He seemed … content. It had been a long, long time since Sans had seen his brother content.

His fingers curled around the sheet covering the machine, the fabric threatening to tear beneath his hold.

They had a life.

Maybe it wasn’t the best life. Maybe it wasn’t anything like what Sans had thought he would ever live. But it was a life. A life without pain and fear. A life where Papyrus was safe. That was what mattered. That was all that ever should have mattered.

It mattered far more than a poring his time and energy over a hopeless task, trying to return to a world his brother wouldn’t even remember.

With as much care as he could muster, he adjusted the sheet so it covered the machine completely. He stepped back, giving it one last long look.

Then he left his lab, locking the door behind him, and went to meet Papyrus for dinner.

*

Sans didn’t know how he found himself standing on one of the catwalks hovering above the lava in the Core.

He knew he had left the house and started walking, without a destination, as he did sometimes when he couldn’t concentrate and had nothing else to do. He was either busy or asleep so much of the time lately that he rarely had the chance to concentrate on anything in particular, but sometimes—rarely—everything would be done and he would be left sitting in the house, listening to Papyrus moving around and trying to focus on him but all he could think about was how different they sounded. How every similarity was overshadowed by two or three more differences.

Little things. Even though he had built the house to look just as he remembered their old one, it would never be exactly the same. The family photos that had hung all over the walls would never reappear. There would only ever be two bedrooms on the second floor. There were no stains in the kitchen from old food fights, no lingering smell of cookies or casseroles days after they were finishing cooking.

He would never wake up to the smell of hot food wafting from the kitchen. He would never taste Papyrus’s nacho casserole, or chocolate lava cake, or macaroni and cheese or stir fries or fruity pies or mashed potatoes or hot chocolate that made the neighbors laugh because _why would you make a hot drink when it was already so hot outside._

He would never poke his head into his dad’s office to see what he was working on on the days he was too busy to spend time with them, but would never send them away if they wanted to sit near him while he worked.

He would never see Alphys’s blushing face as he complimented her latest project, her flustered babbling when he tried to get her to apply to the Royal Science Department, her excited giggles when he encouraged her to talk about about the new anime she had watched.

He would never hear Dr. Frewth making bad jokes that only ever made his dad laugh.

He would never see Dr. Lemming’s gentle grin or see the flash of their camera.

He would never feel Dr. Japer’s soft paws brushing over his skull.

He would never hear his dad’s gentle words of encouragement, pushing him along even when he thought about giving up.

He looked down at the lava, watching it roll and bubble beneath him, and felt his feet carrying him another step forward.

Would there be anything left of his dad down there, if he looked? Would his bones have turned to nothing by now? If he had stayed after he fell, if he had found a way to get down there, could he have pulled him out?

Another step. His toes were hanging over the edge now. Almost every other part of the Core had guard rails now, but not here. No one came here, apparently. No one worked here. No one would be in danger here.

No one would find him here.

Papyrus was okay. He _would_ be okay. He was happy here. Happy enough, anyway. He had a friend, someone who would make sure he was taken care of. He had a home, a home Sans had made sure would never be taken away. He had ambition, and strength, and hope.

He had everything he needed.

And Sans …

He would never see them again. Any of them. His dad or Alphys or Dr. Japer or Dr. Frewth or Dr. Lemming.

Or his brother.

He was never going to fix the machine. And even if he could, that wouldn’t bring anyone back. He would never see his home again. He would never see his friends or his family. He would never get back the life he had lost.

He peered down at the lava, rising and falling in tiny waves, felt its heat wafting through the air. He wondered, just for a second, if it would hurt. But then he could see his dad’s face, and Papyrus’s face, smiling at him, holding their arms out toward him. And he felt his own mouth curling up to match theirs, his eyes soft, his soul heavy.

He was tired.

He was so, so tired.

He just wanted to … to …

“SANS?”

Sans jolted so hard he almost fell over the edge.

But he kept his balance and turned to his left, toward the voice he could never mistake.

And there he was. Standing there, maybe five yards away from him. His eyes wide, his mouth open, his body stiff with confusion and concern.

And suddenly it didn’t matter that he was wearing gloves or that his outfit was nonsensical or that he spoke even louder than the voice Sans remembered. This was his brother. His brother standing there, looking at him with fear and worry, and Sans found himself stepping away from the edge, if only to make a bit of that fear and worry go away.

Papyrus should never be afraid.

Papyrus should be happy.

Always.

“hey, bro,” he said, his voice barely carrying over the sound of whirring machines and bubbling lava below him. He gave his best attempt at a grin, and as he watched Papyrus’s face soften, it wasn’t as hard to manage it as he would have imagined.

Papyrus fidgeted, giving him a slow, hesitant smile back.

“I’M GOING TO MAKE DINNER TONIGHT,” he said. “WHY DON’T YOU … SET THE TABLE?”

It wasn’t meant to be a question, from what Sans could tell, but it sounded like one anyway. As if Papyrus didn’t think he could count on his brother to do something so simple.

Funny. Didn’t he usually just demand that Sans do whatever he asked, especially something so small? When had he started sounding so _hesitant_?

Sans took another step away from the edge, toward Papyrus, giving a slow, yet sure nod.

“k.”

Papyrus’s eyes softened, and his shoulders—which Sans had never seen as tense as they were now—falling. He nodded, too.

They didn’t say anything else. For once, Papyrus was silent as they walked through the Core and back out into Hotland. Only as they left the Core behind them did Sans find himself wondering if Papyrus had ever been to the Core before—in a time he would remember, anyway. He searched his memory, but couldn’t find an answer. He came very close to asking how he knew he would be there, how he knew his way around the intricate inner workings of the massive machine, but stopped himself at the last second.

He didn’t know why, but he wasn’t sure he wanted to know the answer.

After ten minutes of silence, when they had almost reached the bridge leading from Hotland to Waterfall, Papyrus cleared his throat.

I HEARD THERE WAS A JOB OPEN AT THE SENTRY STATION.”

Sans looked up to face him again, browbone furrowed. Papyrus faced ahead, but glanced at him out of the corner of his eye, not quite long enough for Sans to read his expression.

“YOU SHOULD WORK THERE,” he said, and though he seemed to try to make it sound like his usual absolute, confident statements, Sans could just make out the same faint uncertainty lingering behind the words. “IT WOULD BE GOOD FOR YOU.”

Sans turned away again, staring at his feet as they both stepped onto the rickety old bridge. He could still remember almost falling off it when he was a kid, when he was still learning to manage his lack of full vision, and his dad snatching him up and holding him to his chest for ten minutes until they all stopped shaking.

“i’ll check it out.”

He could feel Papyrus looking at him, even though he didn’t turn to look back.

“REALLY?” he asked. Sans tried to speak, but no words came out. Papyrus paused. “ARE YOU REALLY GOING TO DO IT OR ARE YOU JUST SAYING YOU’RE GOING TO DO IT SO I WILL BE HAPPY?”

Sans’s steps slowed, but he picked up his pace quickly enough that he was fairly sure Papyrus didn’t notice. He swallowed against the lump in his throat and allowed himself a glance, just a glance, at his brother, walking beside him. It was just long enough to make out the faint hope gleaming in his eyes.

“i’ll go tomorrow. first thing,” he replied, before he even had the chance to think about it. The corner of his mouth quirked up again in a faint smirk. “you can even wake me up early to make sure i do it.”

Papyrus jerked his head to face him, just as Sans allowed himself to do the same.

“FIRST THING,” Papyrus repeated.

Sans smiled a little wider. “yup.”

Papyrus’s browbone furrowed. He looked Sans up and down, as if somehow scanning him for a lie.

“YOU PROMISE?”

Sans started to speak, then paused, letting his footsteps slow once again, letting himself take in the sight before him. Papyrus. His brother. Staring at him with a faint smile, still suspicious, still uncertain, but hopeful. Always hopeful. Even when things were difficult. Even when the chances of them turning out well were close to none.

It would have been so easy to give up.

It would have been so easy to turn around and run back to the Core.

It would have been so easy to go to sleep and just sleep, forever, refusing to wake up, refusing to _get_ up, just let the world go on and let him stop being a part of it.

It would have been so easy, if he were alone.

But he wasn’t alone.

He would never be alone.

Even if everyone else left … even if he had lost everything else that had ever been important to him … he hadn’t lost everything. He hadn’t lost every _one._

Maybe one person wouldn’t have been enough for everyone. But their one person wasn’t his.

“… yeah,” he replied, the sound quiet and breathy, but as sure as he could get it out.

Papyrus stared for a moment, then broke out into a wide grin, facing ahead again and picking up his pace, and even though he had to struggle to keep up, Sans managed it nonetheless.

Sans loved his brother.

He loved his brother more than anything in the world.

He loved the brother who had helped him drag their dad up the stairs after he collapsed on the couch, the brother who spent thirty minutes writing the message inside a card so that every letter looked perfect, the brother who brought him homemade lunch when he forgot it, the brother who told him he needed to sleep more, the brother who took his place in painful experiments so that _he_ wouldn’t have to go through them. The brother who brought home a human and never stopped fighting to make sure she was safe.

And he loved the brother who couldn’t cook to save his life, who liked goofy, flamboyant outfits, who had accepted the lies another him had told, who had accepted a brother who _wasn’t his_ but who needed him so badly, who couldn’t live without him, who clung to every scrap of happiness they could share as if it was all he had left in the world.

He loved Papyrus.

It didn’t matter which Papyrus it was.

He stared up at his brother, walking proud and tall beside him, and he felt his eyes soften, his smile widen, even if it was painful.

Yes. This was his brother, even if it wasn’t the same one he was used to, even if he might never know which brother this was, or if this one had existed in the same way before all this had happened. He still loved him, and he would still take care of him. Even after all he had lost, even with all he would never get back, he still had his brother. He still had Papyrus. And Papyrus— _this_ Papyrus—still had his whole life ahead of him, and if Sans had anything to say about it, he would have the world laid out at his feet.

And no matter what it took, Sans wasn’t going to miss a second.

**Notes for the Chapter:**

> Well, this is it. I started writing this story about this time a year ago, and now it's finally done. Well. Sort of.
> 
> Thank you so, so much to everyone who has read, commented, bookmarked, and/or left kudos. Your support and kind words mean the world. :)
> 
> And if you've enjoyed this story, I hope you'll stick around for the sequels, starting next Wednesday with the first chapter of _It's Raining In Between_ :
> 
> Two thousand years ago, a young skeleton named Gaster befriended a human.  
> A hundred years ago, a human child fell into the royal family’s life.  
> Ninety years ago, a little boy crashed into the Ruins and broke a mother’s heart.  
> Forty years ago, the Royal Scientist captured a human who wandered into his path.  
>  ~~Sixteen~~ Six years ago, a young skeleton met a fish girl.  
>  Six years ago, another skeleton befriended a voice through a door.
> 
> All the stories, past, present and future, that didn’t fit into _It’s Raining Right Here_.
> 
> And after that, the direct sequel, focusing on Papyrus: _The Flowers are Blooming_ ...

**Works inspired by this one:**

  * [A Stranger In Snowdin](https://archiveofourown.org/works/13134087) by [ReaderRose](https://archiveofourown.org/users/ReaderRose/pseuds/ReaderRose)




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